Azure Security
Notes
Lessons Learned from
Exploring Microsoft Azure and the Cloud Security Space
J.D. Meier, Principal PM, Microsoft
Paul Enfield
Acknowledgments
Thanks to the following external contributors and reviewers:
Adam Grocholski; Andy Eunson; Bill Collette; Christopher Seary; Jason Taylor; John Daniels; Juval Lowy; Kevin Lam; Long Le; Michael Smith; Michael Stiefel; Michele Leroux Bustamante; Norman Headlam; Rockford Lhotka; Rudolph Araujo; Sarang Kulkarni; Steven Nagy; Terrance
Snyder; Will Clevenger Thanks to the following Microsoft contributors and reviewers:
Akshay Aggarwal; Alik Levin; Andreas Fuchsberger; Babur Butter; Bharat Shyam; Dave Brankin; Danny Cohen; Diego Dagum; Don Willits; Eugenio Pace; Gabriel Morgan; Jeff Mueller; John Steer; Julian Gonzalez; Mark Curphey; Mohit Srivastava; Pat Filoteo; Rahul Verma; Raul Rojas;
Scott Densmore; Sesha Mani; Serena Yeoh; Sriram Krishnan; Stefan Schackow; Steve Marx; Stuart Kwan; Terri Schmidt; Tobin Titus; Varun Sharma; Vidya Vrat Agarwal; Vikram Bhambri;
Our Cloud Security Approach
Objectives
• Learn a security frame
• Learn an approach for applying the security frame to application scenarios
• Learn key components of the security approach for these notes
Overview
These notes summarize how we took a look at securing Web applications, web services, and data in the cloud. We basically started by mapping out common application scenarios. We then figured out a way to group threats and attacks into a set of common categories. These categories make it easy for us to analyze and inspect the various parts of an application and engineering decisions. Then we focused on finding common principles, patterns, and practices, while working with customers, field, product teams, and industry experts.
Our Cloud Security Approach in a Nutshell
We took a pragmatic approach to security, identifying key deltas, building on what we know, and leveraging proven practices. Here are some of the cornerstone concepts we used to focus and drive our security efforts:
• Visual Application Scenarios and Solutions. We created simple visuals that show end-to-end scenarios. You can think of these as how you might put on a whiteboard if you were to draw the end in mind for a particular application scenario. This is a simple way to share authentication and authorization patterns for common application scenarios.
• Secure the network, host, and application. Ask any security expert, where the problems are, and they’ll say it’s the stuff that falls between the cracks. Thinking about security holistically across the network, host, and application is the key to both helping you focus your efforts, as well as catching what falls between the cracks.
• Principles, patterns, and practices. Design principles help you leverage proven practices. Rather than have a rule for everything, you have a smaller set of principles to guide you. Patterns are simply problem and solution pairs in context. They help share strategies and principles by building a shared vocabulary. For example, the Trusted Subsystem pattern
the application identity rather than every caller. Practices are simply actions, methods, or techniques. For example, you can use patterns & practices Threat Modeling
your application.
• Threats and countermeasures. One way to make security actionable and prescriptive is to focus on threats and countermeasures. This means identifying the bad things that can happen, and what your defenses, security controls, or countermeasures are.
• Security Frame. There are many ways to chunk up and think about security. For example, you might use C.I.A., where C is confidentiality, I is integrity, and A represent availability. Another approach is to focus on the three A’s: Authentication, Access control, and Auditing. We’ve found it especially useful to use the following categories to organize and share
application security principles, patterns, anti-patterns, and practices: “Auditing and Logging”, “Authentication”, “Authorization”, “Communication”, “Configuration Management”, “Cryptography”, “Exception Management”, “Sensitive Data”, “Session Management”, and “Validation”.
• People, process, and technology. Another way to look at security is through the people, process, and technology viewpoints. You can also use each of these views when you look at security for your network, host, and application.
• Application, Infrastructure, and Business. This is another helpful lens for looking at security. You can look at the principles, patterns, and practices for the application, the infrastructure, or the business. This leads to application security patterns, infrastructure security patterns, and business security patterns and practices.
At the end of the day, what’s important is using the lens that helps you the most, and avoid using the wrong tool for the job, or using a one-size fits all solution. Instead, chunk up the problem, while keeping a holistic view.
How We Got Started
Tackling cloud security can be overwhelming without an approach. In these notes, we have an approach that simplifies and improves security. It does so by chunking up security in a way that helps us leverage proven practices, while sharing information around emerging practices. One way to simplify thinking about security is to simplify the language. When we first started talking with customers about the cloud and security, it was difficult to have meaningful conversations, simply because we didn’t have a shared vocabulary.
Using a threats and countermeasures approach to talk about security is a key step to simplifying cloud security. Basically, we can look through our security lens (our security frame), and look for threats, attacks, vulnerabilities, and countermeasures. We can use that same lens and look for principles, patterns, and anti-patterns. This helps us turn security information into insight and action.
Another important step is leveraging application types from the patterns & practices Application Architecture Guide, second edition -
focus to application scenarios, and represent them visually. Our goal is to show how to secure your Web application, Web services, and data in the cloud visually. With these scenarios we can move to the whiteboard and draw end-to-end scenarios.
By using a security frame, focusing on threats and countermeasures, and visual scenarios, we have an effective backdrop for analyzing, evaluating, and talking about cloud security
challenges.
Threats and Countermeasures Focus
One way to make security actionable and prescriptive is to focus on threats, attacks, vulnerabilities and countermeasures:
• Threat - A potential occurrence malicious or otherwise that may harm an asset.
• Attack - An action taken to harm an asset.
• Vulnerability - A weakness that makes a threat possible.
• Countermeasure - A safeguard that addresses a threat and mitigates risk.
This means identifying the bad things that can happen, and what your defenses, security controls, or countermeasures are. By building a knowledgebase of threats, attacks,
vulnerabilities, and countermeasures, we can dramatically improve our ability to share security know-how.
Example Application Scenario and Solution
Each Visual Scenario and Solution consists of a Scenario, Solution, and Solution Summary Table. The Scenario is a simple visual of the application from a deployment standpoint. The Solution is a visual of how you might address authentication, authorization, and communication (the security runtime patterns.) The Solution Summary Table is a quick description of how you would address the authentication, authorization, and communication from a security standpoint.
Solution
Solution Summary Table
Area Notes
Authentication • Authenticate users with forms authentication • Store users in Azure Tables
• Use TableStorageMembershipProvider for membership API’s • Authenticate application against Azure Storage with access key • Map ASP.NET users to single Azure Storage connection
• All access to the database occurs as the application identity
Authorization • Use TableStorageRoleProvider for roles API’s • Authorize users in application logic
• Store roles in Azure Tables
Communication • Use HTTP port 80 for non-secure connections to ASP.NET application • Perform forms authentication over port 443 (SSL)
Security Frame
A Security Frame acts as a simple lens. It helps organize and share security knowledge in a set of actionable buckets. Here is an explanation of the key buckets used in these notes:
Category Notes
Auditing and Logging How security-related events are recorded, monitored, and audited.
Authentication The process of proving identity, typically through credentials, such as a user name and password
Authorization How your application provides access controls for roles, resources and operations.
Communication How data is transmitted over the wire. Transport security versus message encryption is covered here.
Configuration
Management How your application handles configuration and administration of your applications from a security perspective.
Cryptography How your application enforces confidentiality and integrity.
Exception
Management How you handle applications errors and exceptions.
memory, over the network, or in persistent stores
Session Management A session refers to a series of related interactions between a user and your application.
Validation How your application filters, scrubs, or rejects input before additional processing, or how it sanitizes output.
The key to the buckets is that they are actionable. Another key is that developers can relate to them. This makes it easier to share security knowledge between security experts and
developers in a pragmatic way.
Carrying the Story Forward
Improving Web Application Security: Threats and Countermeasures
solution by addressing key security hotspots defined by the security frame in Figure 1 below. This visual model allows you to conceptualize specific areas and items in an architecture that need to be addressed during the process of securing an application. The visual model
represents a fairly typical on-premise application architecture, and then pins hotspots against it.
Figure 1. Securing the Network, Host and Application – On-premise
Using this visual model concept and the revised security frame for cloud applications we can use the same approach to evaluate cloud applications. In Figure 2 below, we modify the visual
Database Web Server Application Server Database Server Firewall Apps Firewall Apps Host Host
Patches and Updates Services
Protocols
Accounts
Files and Directories Shares
Securing the Host
Host Router Firewall Switch Securing the Network Ports Registry
Auditing and Logging
Threats and Countermeasures Exception Management Parameter Manipulation Sensitive Data Session Management Validation
Auditing and Logging Authentication Authorization Configuration Mgt. Cryptography
model by hosting both the application and data layers in the managed infrastructure, which in this case is the cloud. With a managed infrastructure we can remove checks from our list because they are items handled by the managed infrastructure. For example, a Windows Azure application will not have permissions to create user accounts, or elevate privileges. This
alleviates the need to manage accounts at the host level.
Firewall
Apps
Cloud Host
Threats and Countermeasures Data Application Layer Managed Infrastructure Database Layer
Patches and Updates Services
Protocols
Accounts
Files and Directories Shares
Ports Registry
Auditing and Logging Securing the Host
Cryptography
Exception Management Sensitive Data Session Management Validation
Auditing and Logging Authentication Authorization
Communication
Configuration Management
Securing the Application
Router Firewall Switch Securing the
Network
Figure 2. Securing the Network, Host and Application in the Cloud
The above diagram represents the canonical case architecture. To evaluate other architectures such as ones involving federated identity or hybrid on-premise and cloud implementations, you can use the same approach. Represent your architecture with a base diagram, and overlay the frame on it. Once the frame is overlaid, you can evaluate each item for applicability and quickly scope out categories not needing attention.
Cloud Security Threats and Countermeasures
Objectives
• Learn a security frame that applies to the cloud.
• Learn top threats/attacks, vulnerabilities and countermeasures for each area within the security frame.
• Understand differences between threats, attacks, vulnerabilities and countermeasures.
Overview
It is important to think like an attacker when designing and implementing an application. Putting yourself in the attacker’s mindset will make you more effective at designing mitigations for vulnerabilities and coding defensively. This section is a reference of the security frame, and its pieces pinned against the cloud as a platform. We also present threats, vulnerabilities and countermeasures against the cloud organized by hot spot such that you can see how they relate to each other in each category.
Threats, Attacks, Vulnerabilities, and Countermeasures
This chapter analyzes security from the perspectives of threats, vulnerabilities, attacks, and countermeasures against the cloud. These terms are defined as follows:
• Asset. A resource of value such as the data in a database, data on the file system, or a system resource.
• Threat. A potential occurrence – malicious or otherwise – that can harm an asset.
• Vulnerability. A weakness that makes a threat possible.
• Attack. An action taken to exploit vulnerability and realize a threat.
• Countermeasure. A safeguard that addresses a threat and mitigates risk.
Cloud Security Frame
The following key security concepts provide a frame for thinking about security when designing and architecting Windows Azure applications. Understanding these concepts helps you put core security features such as authentication, authorization, auditing, confidentiality, integrity, and availability in action.
Hot Spot Description
Auditing and
Logging Auditing and logging in Windows Azure refers to how security-related events are recorded, monitored, audited, exposed, compiled & partitioned across multiple cloud instances. Examples include: Who did what and when and on which VM instance?
Authentication Authentication is the process of proving identity, typically through credentials, such as a user name and password. In the cloud this also encompasses
authentication against varying identity stores.
Authorization Authorization in Windows Azure is how your application provides access controls for roles, resources and operations. Authorization strategies might involve standard mechanisms, utilize claims and potentially support a federated model.
Communication Communication encompasses how data is transmitted over the wire. Transport security, message encryption, and point to point communication are covered here.
Configuration
Management Configuration management refers to how your application handles configuration and administration of your applications from a security perspective. Examples include: Who does your application run as? Which databases does it connect to? How is your application administered? How are these settings secured?
Cryptography Cryptography in Windows Azure refers to how your application enforces confidentiality and integrity. Examples include: How are you keeping secrets (confidentiality)? How are you tamper-proofing your data or libraries
(integrity)? How are you providing seeds for random values that must be cryptographically strong? Certificates and cert management are in this domain as well.
Input and Data
Validation Validation refers to how your application filters, scrubs, or rejects input before additional processing, or how it sanitizes output. It's about constraining input through entry points and encoding output through exit points. Message
validation refers to how you verify the message payload against schema, as well as message size, content and character sets. Examples include: How do you know that the input your application receives is valid and safe? Do you trust data from sources such as databases and file shares?
Exception
Management Exception management refers to how you handle applications errors and exceptions. Examples include: When your application fails, what does your application do? Does it support graceful failover to other application instances in the cloud? How much information do you reveal? Do you return friendly error information to end users? Do you pass valuable exception information back to the caller?
Sensitive Data Sensitive data refers to how your application handles any data that must be protected either in memory, over the network, or in persistent stores. Examples include: How does your application handle sensitive data? How is sensitive data shared between application instances?
Threats and Attacks
Category Items
Auditing and
Logging • Disclosure of confidential informationinformation from log files. . An attacker gathers sensitive • Denial of service (DoS). An attacker overwhelms logs with excessive entries
• Repudiation. An attacker denies performing an operation, exploits an application without trace, or covers his or her tracks.
Authentication • Network eavesdropping. An attacker steals identity and/or credentials off the network by reading network traffic not intended for them.
• Brute force attacks. An attacker guesses identity and/or credentials through the use of brute force.
• Dictionary attacks. An attacker guesses identity and/or credentials through the use of common terms in a dictionary designed for that purpose. • Cookie replay attacks. An attacker gains access to an authenticated session
through the reuse of a stolen cookie containing session information. • Credential theft. An attacker gains access to credentials through data theft;
for instance, phishing or social engineering.
Authorization • Elevation of privilege. An attacker enters a system as a lower-level user, but is able to obtain higher-level access.
• Disclosure of confidential data. An attacker accesses confidential information because of authorization failure on a resource or operation. • Data tampering. An attacker modifies sensitive data because of
authorization failure on a resource or operation.
• Luring attacks. An attacker lures a higher-privileged user into taking an action on their behalf. This is not an authorization failure but rather a failure of the system to properly inform the user.
• Token stealing. An attacker steals the credentials or token of another user in order to gain authorization to resources or operations they would not otherwise be able to access.
Communication • Failure to encrypt messages. An attacker is able to read message content off the network because it is not encrypted.
• Theft of encryption keys. An attacker is able to decrypt sensitive data because he or she has the keys.
• Man-in-the-middle attack. An attacker can read and then modify messages between the client and the service.
• Session replay. An attacker steals messages off the network and replays them in order to steal a user's session.
• Data tampering. An attacker modifies the data in a message in order to attack the client or the service
Configuration
Management • Unauthorized access to configuration stores.configuration files and is able to modify binding settings, etc. An attacker gains access to • Retrieval of clear text configuration secrets. An attacker gains access to
configuration files and is able to retrieve sensitive information such as database connection strings.
Cryptography • Encryption cracking. Breaking an encryption algorithm and gaining access to the encrypted data.
• Loss of decryption keys. Obtaining decryption keys and using them to access protected data.
Exception
Management • Information disclosure.through exception information. Sensitive system or application details are revealed • Denial of service. An attacker uses error conditions to stop your service or
• Elevation of privilege. Your service encounters an error and fails to an insecure state; for instance, failing to revert impersonation.
Input and Data
Validation • Canonicalization attacks.validation is performed on a different form of the input than that which is Canonicalization attacks can occur anytime used for later processing. For instance, a validation check may be performed on an encoded string, which is later decoded and used as a file path or URL. • Cross-site scripting. Cross-site scripting can occur if you fail to encode user
input before echoing back to a client that will render it as HTML.
• SQL injection. Failure to validate input can result in SQL injection if the input is used to construct a SQL statement, or if it will modify the construction of a SQL statement in some way.
• Cross-Site Request Forgery: CSRF attacks involve forged transactions submitted to a site on behalf of another party.
• XPath injection. XPath injection can result if the input sent to the Web service is used to influence or construct an XPath statement. The input can also introduce unintended results if the XPath statement is used by the Web service as part of some larger operation, such as applying an XQuery or an XSLT transformation to an XML document.
• XML bomb. XML bomb attacks occur when specific, small XML messages are parsed by a service resulting in data that feeds on itself and grows
exponentially. An attacker sends an XML bomb with the intent of
overwhelming a Web service’s XML parser and resulting in a denial of service attack.
Sensitive Data • Memory dumping. An attacker is able to read sensitive data out of memory or from local files.
• Network eavesdropping. An attacker sniffs unencrypted sensitive data off the network.
• Configuration file sniffing. An attacker steals sensitive information, such as connection strings, out of configuration files.
Vulnerabilities
Category Items
Auditing and
Logging • • Failing to audit failed logons. Failing to secure log files.
• Storing sensitive information in log files. • Failing to audit across application tiers. • Failure to throttle log files.
Authentication • Using weak passwords.
• Storing clear text credentials in configuration files. • Passing clear text credentials over the network. • Permitting prolonged session lifetime.
• Mixing personalization with authentication.
an untrusted network).
Authorization • Relying on a single gatekeeper (e.g., relying on client-side validation only). • Failing to lock down system resources against application identities. • Failing to limit database access to specified stored procedures. • Using inadequate separation of privileges.
• Connection pooling.
• Permitting overprivileged accounts.
Configuration
Management • • Using insecure custom administration interfaces. Failing to secure configuration files on the server. • Storing sensitive information in the clear text. • Having too many administrators.
• Using overprivileged process accounts and service accounts.
Communication • Not encrypting messages. • Using custom cryptography. • Distributing keys insecurely.
• Managing or storing keys insecurely.
• Failure to use a mechanism to detect message replays. • Not using either message or transport security.
Cryptography • Using custom cryptography • Failing to secure encryption keys
• Using the wrong algorithm or a key size that is too small • Using the same key for a prolonged period of time • Distributing keys in an insecure manner
Exception
Management • • Failure to use structured exception handling (try/catch). Revealing too much information to the client. • Failure to specify fault contracts with the client.
• Failure to use a global exception handler.
Input and Data
Validation • • Using non-validated input used to generate SQL queries. Relying only on client-side validation.
• Using input file names, URLs, or usernames for security decisions. • Using application-only filters for malicious input.
• Looking for known bad patterns of input.
• Trusting data read from databases, file shares, and other network resources. • Failing to validate input from all sources including cookies, headers,
parameters, databases, and network resources.
Sensitive Data • Storing secrets when you do not need to. • Storing secrets in code.
• Storing secrets in clear text in files, registry, or configuration. • Passing sensitive data in clear text over networks.
Countermeasures
Auditing and
Logging • • Identify malicious behavior. Know your baseline (know what good traffic looks like).
• Use application instrumentation to expose behavior that can be monitored. • Throttle logging.
• Strip sensitive data before logging.
Authentication • Use strong password policies.
• Do not store credentials in an insecure manner.
• Use authentication mechanisms that do not require clear text credentials to be passed over the network.
• Encrypt communication channels to secure authentication tokens. • Use Secure HTTP (HTTPS) only with forms authentication cookies. • Separate anonymous from authenticated pages.
• Using cryptographic random number generators to generate session IDs.
Authorization • Use least-privileged accounts.
• Tie authentication to authorization on the same tier. • Consider granularity of access.
• Enforce separation of privileges. • Use multiple gatekeepers.
• Secure system resources against system identities.
Configuration
Management • • Using insecure custom administration interfaces. Failing to secure configuration files on the server. • Storing sensitive information in the clear text. • Having too many administrators.
• Using overprivileged process accounts and service accounts.
Communication • Use message security or transport security to encrypt your messages. • Use proven platform-provided cryptography.
• Periodically change your keys.
• Use any platform-provided replay detection features.
• Consider creating custom code if the platform does not provide a detection mechanism.
• Turn on message or transport security.
Cryptography • Do not develop and use proprietary algorithms (XOR is not encryption. Use established cryptography such as RSA)
• Avoid key management.
• Use the RNGCryptoServiceProvider method to generate random numbers • Periodically change your keys
Exception
Management • • Use structured exception handling (by using try/catch blocks). Catch and wrap exceptions only if the operation adds value/information. • Do not reveal sensitive system or application information.
• Implement a global exception handler. • Do not log private data such as passwords.
Sensitive Data • Do not store secrets in software.
• Encrypt sensitive data over the network. • Secure the channel.
• Encrypt sensitive data in configuration files.
• Validate input: length, range, format, and type. • Validate XML streams.
• Constrain, reject, and sanitize input. • Encode output.
• Restrict the size, length, and depth of parsed XML messages.
Threats and Attacks Explained
1. Brute force attacks. Attacks that use the raw computer processing power to try different permutations of any variable that could expose a security hole. For example, if an attacker knew that access required an 8-character username and a 10-character password, the attacker could iterate through every possible (256 multiplied by itself 18 times) combination in order to attempt to gain access to a system. No intelligence is used to filter or shape for likely combinations.
2. Buffer overflows. The maximum size of a given variable (string or otherwise) is exceeded, forcing unintended program processing. In this case, the attacker uses this behavior to cause insertion and execution of code in such a way that the attacker gains control of the program in which the buffer overflow occurs. Depending on the program’s privileges, the seriousness of the security breach will vary.
3. Canonicalization attacks. There are multiple ways to access the same object and an
attacker uses a method to bypass any security measures instituted on the primary intended methods of access. Often, the unintended methods of access can be less secure deprecated methods kept for backward compatibility.
4. Cookie manipulation. Through various methods, an attacker will alter the cookies stored in the browser. Attackers will then use the cookie to fraudulently authenticate themselves to a service or Web site.
5. Cookie replay attacks. Reusing a previously valid cookie to deceive the server into believing that a previously authenticated session is still in progress and valid.
6. Credential theft. Stealing the verification part of an authentication pair (identity + credentials = authentication). Passwords are a common credential.
7. Cross-Site Request Forgery (CSRF). Interacting with a web site on behalf of another user to perform malicious actions. A site that assumes all requests it receives are intentional is vulnerable to a forged request.
8. Cross-site scripting (XSS). An attacker is able to inject executable code (script) into a stream of data that will be rendered in a browser. The code will be executed in the context of the user’s current session and will gain privileges to the site and information that it would not otherwise have.
9. Connection pooling. The practice of creating and then reusing a connection resource as a performance optimization. In a security context, this can result in either the client or server using a connection previously used by a highly privileged user being used for a lower-privileged user or purpose. This can potentially expose vulnerability if the connection is not reauthorized when used by a new identity.
10.Data tampering. An attacker violates the integrity of data by modifying it in local memory, in a data-store, or on the network. Modification of this data could provide the attacker with access to a service through a number of the different methods listed in this document. 11.Denial of service. Denial of service (DoS) is the process of making a system or application
unavailable. For example, a DoS attack might be accomplished by bombarding a server with requests to consume all available system resources, or by passing the server malformed input data that can crash an application process.
12.Dictionary attack. Use of a list of likely access methods (usernames, passwords, coding methods) to try and gain access to a system. This approach is more focused and intelligent than the “brute force” attack method, so as to increase the likelihood of success in a shorter amount of time.
13.Disclosure of sensitive/confidential data. Sensitive data is exposed in some unintended way to users who do not have the proper privileges to see it. This can often be done through parameterized error messages, where an attacker will force an error and the program will pass sensitive information up through the layers of the program without filtering it. This can be personally identifiable information (i.e., personal data) or system data.
14.Elevation of privilege. A user with limited privileges assumes the identity of a privileged user to gain privileged access to an application. For example, an attacker with limited privileges might elevate his or her privilege level to compromise and take control of a highly privileged and trusted process or account. More information about this attack in the
context of Windows Azure can be found in the Security Best Practices for Developing Windows Azure Applications at
15.Encryption. The process of taking sensitive data and changing it in such a way that it is unrecognizable to anyone but those who know how to decode it. Different encryption methods have different strengths based on how easy it is for an attacker to obtain the original information through whatever methods are available.
16.Information disclosure. Unwanted exposure of private data. For example, a user views the contents of a table or file that he or she is not authorized to open, or monitors data passed in plaintext over a network. Some examples of information disclosure vulnerabilities include the use of hidden form fields, comments embedded in Web pages that contain database connection strings and connection details, and weak exception handling that can lead to internal system-level details being revealed to the client. Any of this information can be very useful to the attacker.
17.Luring attacks. An attacker lures a higher-privileged user into taking an action on his or her behalf. This is not an authorization failure but rather a failure of the system to properly inform the user.
18.Man-in-the-middle attacks. A person intercepts both the client and server communications and then acts as an intermediary between the two without each ever knowing. This gives the “middle man” the ability to read and potentially modify messages from either party in order to implement another type of attack listed here.
19.Network eavesdropping. Listening to network packets and reassembling the messages being sent back and forth between one or more parties on the network. While not an attack itself, network eavesdropping can easily intercept information for use in specific attacks listed in this document.
20.Open Redirects. Attacker provides a URL to a malicious site when allowed to input a URL used in a redirect. This allows the attacker to direct users to sites that perform phishing attacks or other malicious actions.
21.Password cracking. If the attacker cannot establish an anonymous connection with the server, he or she will try to establish an authenticated connection. For this, the attacker must know a valid username and password combination. If you use default account names, you are giving the attacker a head start. Then the attacker only has to crack the account’s password. The use of blank or weak passwords makes the attacker’s job even easier. 22.Repudiation. The ability of users (legitimate or otherwise) to deny that they performed
specific actions or transactions. Without adequate auditing, repudiation attacks are difficult to prove.
23.Session hijacking. Also known as man-in-the-middle attacks, session hijacking deceives a server or a client into accepting the upstream host as the actual legitimate host. Instead, the upstream host is an attacker’s host that is manipulating the network so the attacker’s host appears to be the desired destination.
24.Session replay. An attacker steals messages off of the network and replays them in order to steal a user’s session.
25.Session fixation. An attacker sets (fixates) another person’s session identifier artificially. The attacker must know that a particular Web service accepts any session ID that is set
externally; for example, the attacker sets up a URL such as
http://unsecurewebservice.com/?sessionID=1234567. The attacker then sends this URL to a valid user, who clicks on it. At this point, a valid session with the ID 1234567 is created on the server. Because the attacker determines this ID, he or she can now hijack the session, which has been authenticated using the valid user’s credentials.
26.Spoofing. An attempt to gain access to a system by using a false identity. This can be accomplished by using stolen user credentials or a false IP address. After the attacker successfully gains access as a legitimate user or host, elevation of privileges or abuse using authorization can begin.
27.SQL injection. Failure to validate input in cases where the input is used to construct a SQL statement or will modify the construction of a SQL statement in some way. If the attacker can influence the creation of a SQL statement, he or she can gain access to the database with privileges otherwise unavailable and use this in order to steal or modify information or destroy data.
28.Throttling. The process of limiting resource usage to keep a particular process from bogging down and/or crashing a system. Relevant as a countermeasure in DoS attacks, where an attacker attempts to crash the system by overloading it with input.
Countermeasures Explained
1. Assume all input is malicious. Assuming all input is malicious means designing your
application to validate all input. User input should never be accepted without being filtered and/or sanitized.
2. Audit and log activity through all of the application tiers. Log business critical and security sensitive events. This will help you track security issues down and make sense of security problems. Skilled attackers attempt to cover their tracks, so you’ll want to protect your logs.
3. Avoid storing secrets. Design around storing secrets. If necessary, sometimes they can be avoided by storing them after using a one-way hash algorithm.
4. Avoid storing sensitive data in the Web space. Anything exposed to the public Internet is considered “web space.” Sensitive data stored in a location that might be compromised by any member of the public places it at much higher risk.
5. Back up and regularly analyze log files. Some attacks can occur over time. Regular analysis of logs will allow you to recognize with sufficient time to address them. Performing regular backups lowers the risk of an attacker covering his tracks by deleting logging of his activities. 6. Be able to disable accounts. The ability to reactively defend an attack by shutting out a user
should be supported through the ability to disable an account.
7. Be careful with canonicalization issues. Predictable naming of file resources is convenient for programming, but is also very convenient for malicious parties to attack. Application logic should not be exposed to users in this manner. Instead, you use file names derived from the original names or fed through a one-way hashing algorithm.
8. Catch exceptions. Unhandled exceptions are at risk of passing too much information to the client. Handle exceptions when possible.
9. Centralize your input and data validation. Input and data validation should be performed using a common set of code such as a validation library.
10.Consider a centralized exception management framework. Exception handling frameworks are available publically and provide an established and tested means for handling
exceptions.
11.Consider authorization granularity. Every object needs to have an authorization control that authorizes access based on the identity of the authenticated party requesting access. Fine grained authorization will control access to each resource, while coarse grained authorization will control access to groups of resources or functional areas of the application.
12.Consider identity flow. Auditing should be traceable back to the authenticated party. Take note of identity transitions imposed by design decisions like impersonation.
13.Constrain input. Limit user input to expected ranges and formats.
14.Constrain, reject, and sanitize your input. Constrain, reject and sanitize should be primary techniques in handling input data.
16.Disable anonymous access and authenticate every principle. When possible, require all interactions to occur as an authenticated party as opposed to an anonymous one. This will help facilitate more effective auditing.
17.Do not develop your own cryptography. Custom cryptography is not difficult for experts to crack. Established cryptography is preferred because it is known to be safe.
18.Do not leak information to the client. Exception data can potentially contain sensitive data or information exposing program logic. Provide clients only with the error data they need for the UI.
19.Do not log private data such as passwords. Log files are an attack vector for malicious parties. Limit the risk of their being compromised by not logging sensitive data in the log. 20.Do not pass sensitive data using the HTTP-GET protocol. Data passed using HTTP GET is
appended to the querystring. When users share links by copying and pasting them from the browser address bar, sensitive data may also be inadvertently passed. Pass sensitive data in the body of a POST to avoid this.
21.Do not rely on client-side validation. Any code delivered to a client is at risk of being compromised. Because of this, it should always be assumed that input validation on the client might have been bypassed.
22.Do not send passwords over the wire in plaintext. Authentication information
communicated over the wire should always be encrypted. This may mean encrypting the values, or encrypting the entire channel with SSL.
23.Do not store credentials in plaintext. Credentials are sometimes stored in application configuration files, repositories, or sent over email. Always encrypt credentials before storing them.
24.Do not store database connections, passwords, or keys in plaintext. Configuration secrets should always be stored in encrypted form, external to the code.
25.Do not store passwords in user stores. In the event that the user store is compromised, an attack should never be able to access passwords. A derivative of a password should be stored instead. A common approach to this is to encrypt a version of the password using a one-way hash with a SALT. Upon authentication, the encrypted password can be re-generated with the SALT and the result can be compared to the original encrypted password.
26.Do not store secrets in code. Secrets such as configuration settings are convenient to store in code, but are more likely to be stolen. Instead, store them in a secure location such as a secret store.
27.Do not store sensitive data in persistent cookies. Persistent cookies are stored client-side and provide attackers with ample opportunity to steal sensitive data, be it through
encryption cracking or any other means.
28.Do not trust fields that the client can manipulate (query strings, form fields, cookies, or HTTP headers). All information sent from a client should always be assumed to be
malicious. All information from a client should always be validated and sanitized before it is used.
29.Do not trust HTTP header information. Http header manipulation is a threat that can be mitigated by building application logic that assumes HTTP headers are compromised and validates the HTTP headers before using them.
30.Encrypt communication channels to protect authentication tokens. Authentication tokens are often the target of eavesdropping, theft or replay type attacks. To reduce the risk in these types of attacks, it is useful to encrypt the channel the tokens are communicated over. Typically this means protecting a login page with SSL encryption.
31.Encrypt sensitive cookie state. Sensitive data contained within cookies should always be encrypted.
32.Encrypt the contents of the authentication cookies. In the case where cookies are
compromised, they should not contain clear-text session data. Encrypt sensitive data within the session cookie.
33.Encrypt the data or secure the communication channel. Sensitive data should only be passed in encrypted form. This can be accomplished by encrypting the individual items that are sent over the wire, or encrypting the entire channel as with SSL.
34.Enforce separation of privileges. Avoid building generic roles with privileges to perform a wide range of actions. Roles should be designed for specific tasks and provided the minimum privileges required for those tasks.
35.Enforce unique transactions. Identify each transaction from a client uniquely to help prevent replay and forgery attacks.
36.Identify malicious behavior. Monitoring site interactions that fall outside of normal usage patterns, you can quickly identify malicious behavior. This is closely related to “Know what good traffic looks like.”
37.Keep unencrypted data close to the algorithm. Use decrypted data as soon as it is decrypted, and then dispose of it promptly. Unencrypted data should not be held in memory in code.
38.Know what good traffic looks like. Active auditing and logging of a site will allow you know recognize what regular traffic and usage patterns are. This is a required step in order to be able to identify malicious behavior.
39.Limit session lifetime. Longer session lifetimes provide greater opportunity for Cross-Site Scripting or Cross-Site Request Forgery attacks to add activity onto an old session.
40.Log detailed error messages. Highly detailed error message logging can provide clues to attempted attacks.
41.Log key events. Profile your application and note key or sensitive operations and/or events, and log these events during application operation.
42.Maintain separate administration privileges. Consider granularity of authorization in the administrative interfaces as well. Avoid combining administrator roles with distinctly different roles such as development, test or deployment.
43.Make sure that users do not bypass your checks. Bypassing checks can be accomplished by canonicalization attacks, or bypassing client-side validation. Application design should avoid exposing application logic, and segregating application logic into flow that can be
interrupted. For example, an ASPX page that performs only validations and then redirects. Instead, validation routines should be tightly bound to the data they are validating.
44.Pass Forms authentication cookies only over HTTPS connections. Cookies are at risk of theft and replay type attacks. Encrypting them with SSL helps reduce the risk of these types of attacks.
45.Protect authentication cookies. Cookies can be manipulated with Cross-Site Scripting attacks, encrypt sensitive data in cookies, and use browser features such as the HttpOnly cookie attribute.
46.Provide strong access controls on sensitive data stores. Access to secret stores should but authorized. Protect the secret store as you would other secure resources by requiring authentication and authorization as appropriate.
47.Reject known bad input. Rejecting known bad input involves screening input for values that are known to be problematic or malicious. NOTE: Rejecting should never be the primary means of screening bad input, it should always be used in conjunction with input
sanitization.
48.Require strong passwords. Enforce password complexity requirement by requiring long passwords with a combination of upper case, lower case, numeric and special (for example punctuation) characters. This helps mitigate the threat posed by dictionary attacks. If possible, also enforce automatic password expiry.
49.Restrict user access to system-level resources. Users should not be touching system resources directly. This should be accomplished through an intermediary such as the application. System resources should be restricted to application access.
50.Retrieve sensitive data on demand. Sensitive data stored in application memory provides attackers another location they can attempt to access the data. Often this data is used in unencrypted form also. To minimize risk of sensitive data theft, sensitive data should be used immediately and then cleared from memory.
51.Sanitize input. Sanitizing input is the opposite of rejecting bad input. Sanitizing input is the process of filtering input data to only accept values that are known to be safe. Alternatively, input can be rendered innocuous by converting it to safe output through output encoding methods.
52.Secure access to log files. Log files should only be accessible to administrators, auditors, or administrative interfaces. An attacker with access to the logs might be able to glean
sensitive data or program logic from logs.
53.Secure the communication channel for remote administration. Eavesdropping and replay attacks can target administration interfaces as well. If using a web based administration interface, use SSL.
54.Secure your configuration store. The configuration store should require authenticated access and should store sensitive settings or information in an encrypted format.
55.Secure your encryption keys. Encryption keys should be treated as secrets or sensitive data. They should be secured in a secret store or key repository.
56.Separate public and restricted areas. Applications that contain public front-ends as well as content that requires authentication to access should be partitioned in the same manner. Public facing pages should be hosted in a separate file structure, directory or domain from private content.
57.Store keys in a restricted location. Protect keys with authorization policies.
58.Support password expiration periods. User passwords and account credentials are
commonly compromised. Expiration policies help mitigate attacks from stolen accounts, or disgruntled employees who have been terminated.
59.Use account lockout policies for end-user accounts. Account login attempts should have a cap on failed attempts. After the cap is exceeded the account should prevent further login attempts. Lockout helps prevent dictionary and brute force attacks.
60.Use application instrumentation to expose behavior that can be monitored: Application transactions that are more likely to be targeted by malicious interactions should be logged or monitored. Examples of this might be adding logging code to an exception handler, or logging individual API calls. By providing a means to watch these transactions you have a higher likelihood of being able to identify malicious behavior quickly.
61.Use authentication mechanisms that do not require clear text credentials to be passed over the network: A variety of authentication approaches exist for use with web based applications some involve the use of tokens while others will pass user credentials (user name/id and password) over the wire. When possible, it is safer to use an authentication mechanism that does not pass the credentials. If credentials must be passed, it is preferable to encrypt them, and/or send them over an encrypted channel such as SSL.
62.Use least privileged accounts. The privileges granted to the authenticated party should be the minimum required to perform all required tasks. Be careful of using existing roles that have permissions beyond what is required.
63.Use least privileged process and service accounts. Allocate accounts specifically for process and service accounts. Lock down the privileges of these accounts separately from other accounts.
64.Use multiple gatekeepers. Passing the authentication system should not provide a golden ticket to any/all functionality. System and/or application resources should have restricted levels of access depending on the authenticated party. Some design patterns might also enforce multiple authentications, sometimes distributed through application tiers.
65.Use SSL to protect session authentication cookies. Session authentication cookies contain data that can be used in a number of different attacks such as replay, Cross-Site Scripting or Cross-Site Request Forgery. Protecting these cookies helps mitigate these risks.
66.Use strong authentication and authorization on administration interfaces. Always require authenticated access to administrative interfaces. When applicable, also enforce separation of privileges within the administrative interfaces.
67.Use structured exception handling. A structured approach to exception handling lowers the risk of unexpected exceptions from going unhandled.
68.Use the correct algorithm and correct key length. Different encryption algorithms are preferred for varying data types and scenarios.
69.Use tried and tested platform features. Many cryptographic features are available through the .NET Framework. These are proven features and should be used in favor of custom methods.
70.Validate all values sent from the client. Similar to not relying on client-side validation, any input from a client should always be assumed to have been tampered with. This input should always be validated before it is used. This encompasses user input, cookie values, HTTP headers, and anything else that is sent over the wires from the client.
71.Validate data for type, length, format, and range. Data validation should encompass these primary tenets. Validate for data type, string lengths, string or numeric formats, and
SDL Considerations
• For more information on preferred encryption algorithms and key lengths, see the Security
Design Guidelines for Improving Cloud Application Security
Overview
While many of the same security patterns and practices you apply to applications you run on-premise, also apply to the cloud, you do need to think about how the context changes some things. For example, running in the cloud means running your applications and data in an environment where you trade control for economic or technical benefits.
Applications running in the cloud by their nature are Internet facing. Deployment patterns change including where you run your code, and how it makes calls to other services or applications. Running in the cloud means thinking in terms of virtualized resources. It also means restricted access to some underlying system resources. Additionally, it means thinking about the interfaces you expose, how you protect them, and the communication protocols you use.
Running in the cloud also means rethinking security context, as well as identity management and access controls, and considering approaches that allow you to integrate, leverage, and interoperate with your existing resources or other services or systems in the cloud, or even with on-premise systems and services.
For a synopsis view of changes to development introduced with Windows Azure, see the What’s New with Windows Azure Cheat Sheet in the Appendix.
Windows Azure and Windows Identity Framework Impact
The following are points that will help you think about how Windows Azure and how Windows Identity Framework may impact your security design:
• Claims -- You can use claims for identity management and for access control. Claims align well with cloud applications because they allow you to factor out identity management logic from your application and integrate with identity providers such as an on-premise Active Directory via Active Directory Federation Services.
• VM model and trust -- The Windows Azure security model is centered around strict control over VMs imposed by two Windows Azure specific trust policies which are defined as full and partial trust. These policies limit access to system resources to prohibit common attacks like elevation of privilege. A working knowledge of what level of permissions are available is required to know which pieces of an existing application can be migrated and which must be adjusted to work under more restrictive permissions.
For more information on full trust in Azure, see
• Azure Storage and SQL Azure -- Some of the things to think about in Windows Azure
regarding data include deciding where to host your data, what will be used to host the data, and what the means of access to that data will be. You can use on-premise data and expose it as a service to your Windows Azure application. Data hosting in the cloud can be done primarily through Windows Azure Storage or SQL Azure. Data exposed to other applications or services should be exposed as a service (Data as a Service), but data consumed only by your application has the option of being accessed without a service interface.
• Deployment -- Deploying the Windows Azure can potentially mean deploying across multiple data centers that are physically separate. This will influence application design patterns, deployment, as well as communication between application pieces. Be aware of your application boundaries, and use resources within the same data center when possible, and communication options such as internal endpoints when applicable.
Architecture and Design Issues for Cloud Applications
When you design for the cloud, keep the following guidelines in mind:
• Factor authentication and authorization logic from application logic. • Use claims based authentication to integrate with existing user stores. • Know the Windows Azure trust policy restrictions.
• Consider your storage options: Windows Azure Storage, SQL Azure, Azure Drives. • Know the communication changes.
Factor authentication and authorization logic from application logic
Implementing authentication and authorization logic based on claims allows you to decouple your application logic from your identity logic. This provides for more secure applications by standardizing around a common implementation of authentication logic around the WS-* protocols. Having the identity logic separate makes the application more maintainable too, by allowing updates or changes to authentication logic that does not impact the application. Building around the WS-* protocols also provides for better interoperability.
Use claims based authentication to integrate with existing user stores
Established approaches to authentication and authorization are still valid in the cloud, but claims and Single Sign-On (SSO) approaches provide strong integration with Active Directory based authentication and federated identity. It is still possible to implement authentication using ASP.NET forms authentication but this will involve creating a new user store. To leverage an existing user store, or integrate with foreign user stores or an on-premise Active Directory, you will want to use the Windows Identity Federation to use the WS-* protocols for a claims based authentication solution.
Know the Windows Azure trust policy restrictions
Code operating in a Windows Azure VM will operate with a more restrictive set of permissions. The default is full trust which still contains a more restrictive set of permissions than an on-premise solution. Some of the most prominent restrictions include the limited access to the registry, and some basic file access restrictions as well. Avoid API's that require system level permissions, or access to Operating System resources. Use internet friendly protocols for service calls, and internal endpoints or queues for IPC.
Consider your storage options: Windows Azure Storage, SQL Azure, Azure
Drives
Windows Azure Storage and SQL Azure are the 2 primary storage options for Windows Azure applications. Azure drives offer another option for persisting information, by writing to the VM's virtual drive, and persisting the drive state to Azure Drives. SQL Azure offers relational data storage and a host for existing TSQL logic. Windows Azure storage offers a lower cost per megabyte stored.
Know the communications changes
Working inside of the Windows Azure data centers influences application design, from the communication standpoint, in a number of ways. VM's are exposed to the public internet as a sub-domain off of the cloudapp.net domain. This means a singular IP address will represent a web role, but the Windows Azure load balancer will resolve the traffic to a VM represented by a virtual IP address. Applications should not be designed with VM instances that depend on specific IP addresses.
Be aware of network communication inside and outside of the Windows Azure data centers. You can gain better performance by taking advantage of the higher bandwidth communications within a data center, as opposed to reaching outside of the data center for services. This
becomes important because the latency introduced at this level can be exploited by attackers in Denial of Service attacks.
Know that internal endpoints for Windows Azure roles exist that allow roles to perform IPC within the data center using TCP based protocols. Both web and worker roles can expose endpoints for tightly bound IPC, whereas Windows Azure Storage queues can be used for loosely bound IPC. The following diagram represents a typical application of queues to perform IPC.
Web Role Load Balance r VMs VMs Worker Role HTTP / HTTPs Storage Message Message Message Queue
IIS Write Read
Figure 1. Windows Azure Storage queues for IPC – Typical model
Potential Application Security Vulnerabilities Summary
Hot Spot Description
Auditing and Logging Attacks made without a trace, unauthorized access to logs or audits, covering tracks by removing audit or log events.
Authentication Identity spoofing, password cracking, elevation of privileges, and unauthorized access.
Authorization Access to confidential or restricted data, tampering, and execution of unauthorized operations.
Communication Eavesdropping, sniffing, replay attacks.
Configuration
Management Unauthorized access to administration interfaces, ability to update configuration data, and unauthorized access to user accounts and account profiles.
Cryptography Access to confidential data or account credentials, or both.
Input and Data
Validation Attacks performed by embedding malicious strings in query strings, form fields, cookies, and HTTP headers. These include command execution, cross-site scripting (XSS), SQL injection, and buffer overflow attacks.
Exception
Management Denial of service and disclosure of sensitive system level details. Sensitive Data.
Sensitive Data Confidential information disclosure and data tampering.
Data Centers and Distribution
Windows Azure data centers exist in pairs for each continental area supported. The Windows Azure Portal allows you to specify which data center to deploy your application to. This
becomes particularly important for applications that are not deployed as a single package. For example, if you deploy a web service to one data center, and then deploy an application that uses that service in a different data center, you will experience more latency than if both are deployed to the same data center. Also note that network traffic within a single data center will be at a much higher level of performance than traffic that must reach the public Internet. Consider the geographic location for your users when deciding which data center(s) to deploy to. Determine which data center has the best network response times for your users and deploy your application to this data center. For example, if your users mostly live in Ohio, the Northern US data center located in Chicago will most likely offer the best response times for these users. Confirm that network performance is superior from this data center, and deploy to it.
Deployment packages are typically built from Visual Studio projects. A Visual Studio project can contain any number of roles. Roles deployed as part of a single deployment package will be deployed as a group and distributed in the data center in fairly close proximity to provide optimal performance. The following diagram represents what a deployment in a single data center might encompass.
Windows Azure
Web RoleWeb Role Web RoleWeb Role Web Role Presentation Layer ASP.NET UI Web Role Services Layer Service Interfaces 80 80
Worker RoleWorker RoleWorker Role
Business Layer
Data Layer
Browser Mobile Rich Client
Silverlight
Front-end Silverlight Front-end
Silverlight Front-end SQL Azure or Azure Storage SQL Azure or Azure Storage SQL Azure or Azure Storage
Figure 2. Single data center deployment application architecture
Locations for SQL Azure and Windows Azure Storage can be specified when establishing the services. It is beneficial to specify the same data center for your application as you use for your data.
Keep these things in mind when securing your Windows Azure application, and remember that it is significantly easier to eavesdrop on traffic on the public Internet than it would be to
compromise security within an Azure data center and sniff traffic inside the data center.
Internal versus External Traffic
Windows Azure meters data transfer for billing. Metering is performed on traffic entering and leaving the data center, but not inside the data center. Systems comprising of parts that must communicate between VMs, should be deployed to the same data center to optimize
expenditures.
Be aware of Windows Azure affinity groups. Affinity groups tell Windows Azure to deploy applications in similar areas within the data center. Doing this will minimize the number of network hops within a data center and improve network performance for your application.
Separation of Responsibilities and Deployment Environments
Separation of responsibilities should be considered for any Windows Azure deployment. This means you should have clear policies defined for the roles of administrator, release manager, developer, tester and any other appropriate role.
The Windows Azure Portal is accessible via 2 methods. A user interface that requires a Live ID to access, and deployment API’s that require a deployment certificate. Multiple deployment certificates can be added to a Windows Azure account. These certificates can be added to Visual Studio and allow multiple distinct parties to deploy from Visual Studio to Windows Azure. Because the Windows Azure Portal access is controlled by Live ID and deployment certificates, policies should be established and include proper management and distribution of both the Live ID and the deployment certificates. Developers should not be in charge of deployment, nor management of the Windows Azure service. Test environments should be deployed separately from production and staging environments.
Note that separation of deployment rights between staging and production environments will prohibit the use of the Virtual IP (VIP) swapping feature in the Windows Azure Portal. This feature allows you to instantly make your staging environment live. The VIP swapping feature requires that both the deployment and staging deployments be under the same Windows Azure Account.
Auditing and Logging
Auditing and logging involves the handling of security related events. Processes for storing the events, monitoring them, and auditing the logs are covered here. Windows Azure introduces some additional considerations in this area due to changes in the logging systems and methods for persisting the logs to permanent storage. Windows Azure applications will also need to build methods for monitoring application health and providing notifications.
The following practices improve your application's auditing and logging:
• Protect your logs. • Consider identity flow.
• Audit and log access across the application. • Sanitize data before logging.
• Back up and analyze logs regularly.
Protect your logs.
Auditing and logging in Windows Azure must be performed to a location that can be secured and persisted. Event logging can be performed to Windows Azure's Monitoring Data Service. Logs should then be persisted into a secure storage location such as Windows Azure Storage. When persisting logs to storage, be sure to implement strong authentication and authorization
against that storage location. Also be aware that access to Windows Azure storage will be via the RESTful interfaces and should therefore be secured over SSL.
For more information about auditing and logging, see the Security Best Practices for Developing Windows Azure Applications at
Consider identity flow.
In Windows Azure, application architectures will commonly flow identities through a common channel. Examples of this would be users authenticating against a web site, and data access to Windows Azure Storage occurring over a common connection, or a common connection string for SQL Azure. Be aware of this identity flow, and be sure to have a way of mapping data access back to the authenticated user. This might be accomplished by passing a user identifier with the data access and storing this with the transaction. Be sure to protect the identifier with a one-way hash if it is not passed over an encrypted channel.
Audit and log across the application.
Audits and logged events should occur at all levels of the application. When implementing logging, be aware of the implications of excessive logging. Excessive logging can lead to
degradation of performance and might be exploited to cause a failure in the service in a Denial of Service attack. In cases where extensive logging may be required for debugging purposes, consider implementing logging levels that can be configured through an administrative
interface. This allows you to obtain detailed logs when required, but not degrade performance when debugging isn’t being performed.
Be sure to log at all locations in code where authentication or authorization takes place. Additionally, be sensitive to transitions in identity such as using a common identity to connect to a web service such as with a WCF binding using a server certificate for service authentication.
Review your application logic flow for key events, and be sure to log these events. Be sure to log both success and failure events.
Include enough information in your logs to reconstruct the user interaction across all levels of the site. With a site that is potentially logging events from several different requests at the same time, it is important to be able to associate log events together. A common means of accomplishing this is to assign a log identifier to be included with all logged events for a particular transaction. Doing this allows you to filter the log based on an id to reconstruct the event flow. Do not use a session id or other sensitive information for this identifier.
