CRV2 FrameworkSpecIssuesASPNetManagedCode

=Code Review Manage Code=

.NET Managed code is less vulnerable to common vulnerabilities found in unmanaged code such as Buffer Overflows and memory corruption however there could be issues in the code that can affect performance and security. The following is a summary of the recommended practices to look for during the code review. Also, it is worth mentioning some tools that can make the work easier on this part and they can help you understand and pin point flaws in your code

Code Access Security
This supports the execution of semi-trusted code, preventing several forms of security threats. The folloowing is a summary of possible vulnerabilities due to improper use of Code Access security:

Declarative security
Use declarative security instead of imperative whenever possible. Example of declarative syntax(MSDN, 2013):

[MyPermission(SecurityAction.Demand, Unrestricted = true)] public class MyClass {  public MyClass {     //The constructor is protected by the security call. }  public void MyMethod {     //This method is protected by the security call. }  public void YourMethod {     //This method is protected by the security call. } }

Unmanaged code
Even though C# is a strong type language, it is possible to use unmanaged code calls by using the ‘unsafe’ code. “Check that any class that uses an unmanaged resource, such as a database connection across method calls, implements the IDisposable interface. If the semantics of the object are such that a Close method is more logical than a Dispose method, provide a Close method in addition to Dispose”.

Exception handling
Manage code should use exception handling for security purposes among other reasons. Make sure that you follow these recommendations:


 * Avoid exception handling in loops, use try/catch block if it is necessary.
 * Identify code that swallows exceptions
 * Use exceptions handling for unexpected conditions and not just to control the flow in the application

FxCop
FxCop is an analysis tool that analyses binary assemblies, not source code. The tool has a predefined set of rules and it is possible to configure and extend them. Some of the available rules regarding security are(CodePlex, 2010):

EnableEventValidationShouldBeTrue Verifies if the EnableEventValidation directive is disabled on a certain page

ValidateRequestShouldBeEnabled Verifies if the ValidateRequest directive is disabled on a certain page.

ViewStateEncryptionModeShouldBeAlways Verifies if the ViewStateEncryptionMode directive is not set to Never on a certain page.

EnableViewStateMacShouldBeTrue Verifies if the EnableViewStateMac directive is not set to false on a certain page.

EnableViewStateShouldBeTrue Verifies if the EnableViewState directive is not set to false on a certain page.

ViewStateUserKeyShouldBeUsed Verifies if the Page.ViewStateUserKey is being used in the application to prevent CSRF.

DebugCompilationMustBeDisabled Verifies that debug compilation is turned off. This eliminates potential performance and security issues related to debug code enabled and additional extensive error messages being returned.

CustomErrorPageShouldBeSpecified Verifies that the CustomErrors section is configured to have a default URL for redirecting uses in case of error.

FormAuthenticationShouldNotContainFormAuthenticationCredentials Verifies that no credentials are specified under the form authentication configuration.

EnableCrossAppRedirectsShouldBeTrue Verifies that system.web.authentication.forms enableCrossAppRedirects is set to true. The settings indicate if the user should be redirected to another application url after the authentication process. If the setting is false, the authentication process will not allow redirection to another application or host. This helps prevent an attacker to force the user to be redirected to another site during the authentication process. This attack is commonly called Open redirect and is used mostly during phishing attacks.

FormAuthenticationProtectionShouldBeAll Verifies that the protection attribute on the system.web.authentication.forms protection is  set to All which specifies that the application use both data validation and encryption to \ help protect the authentication cookie.

FormAuthenticationRequireSSLShouldBeTrue Verifies that the requireSSL attribute on the system.web.authentication.forms configuration element is set to True which forces the authentication cookie to specify the secure attribute. This directs the browser to only provide the cookie over SSL.

FormAuthenticationSlidingExpirationShouldBeFalse Verifies that system.web.authentication.forms slidingExpiration is set to false when the site is being served over HTTP. This will force the authentication cookie to have a fixed timeout value instead of being refreshed by each request. Since the cookie will traverse over clear text network and could potentially be intercepted, having a fixed timeout value on the cookie will limit the amount of time the cookie can be replayed. If the cookie is being sent only over HTTPS, it is less likely to be intercepted and having the slidingExpiration setting to True will cause the timeout to be refreshed after each request which gives a better user experience.

HttpCookiesHttpOnlyCookiesShouldBeTrue Verifies that the system.web.httpCookies httpOnlyCookies configuration setting is set to True which forces all cookies to be sent with the HttpOnly attribute.

HttpCookiesRequireSSLShouldBeTrue Verifies that the system.web.httpCookies requireSSL configuration is set to True which forces all cookies to be sent with the secure attribute. This indicates the browser to only provide the cookie over SSL.

TraceShouldBeDisabled Verifies that the system.web.trace enabled setting is set to false which disables tracing. It is recommended to disable tracing on production servers to make sure that an attacker cannot gain information from the trace about your application. Trace information can help an attacker probe and compromise your application.

AnonymousAccessIsEnabled Looks in the web.config file to see if the authorization section allows anonymous access.

RoleManagerCookieProtectionShouldBeAll Verifies that the system.web.rolemanager cookieProtection is set to All which enforces the cookie to be both encrypted and validated by the server.

RoleManagerCookieRequireSSLShouldBeTrue Verifies that the system.web.rolemanager cookieRequireSSL attribute is set to True which forces the role manager cookie to specify the secure attribute. This directs the browser to only provide the cookie over SSL.

RoleManagerCookieSlidingExpirationShouldBeTrue Verifies that the system.web.rolemanager cookieSlidingExpiration is set to false when the site is being served over HTTP. This will force the authentication cookie to have a fixed timeout value instead of being refreshed by each request. Since the cookie will traverse over clear text network and could potentially be intercepted, having a fixed timeout value on the cookie will limit the amount of time the cookie can be replayed. If the cookie is being sent only over HTTPS, it is less likely to be intercepted and having the slidingExpiration setting to True will cause the timeout to be refreshed after each request which gives a better user experience.

PagesEnableViewStateMacShouldBeTrue Verifies that the viewstate mac is enabled.

PagesEnableEventValidationMustBeTrue Verifies that event validation is enabled.

HttpRuntimeEnableHeaderCheckingShouldBeTrue Verifies that the system.web.httpRuntime enableHeaderChecking attribute is set to true. The setting indicates whether ASP.NET should check the request header for potential injection attacks. If an attack is detected, ASP.NET responds with an error. This forces ASP.NET to apply the ValidateRequest protection to headers sent by the client. If an attack is detected the application throws HttpRequestValidationException.

PagesValidateRequestShouldBeEnabled Verify that validateRequest is enabled.

PagesViewStateEncryptionModeShouldBeAlways Verifies that the viewstate encryption mode is not configured to never encrypt.

CustomErrorsModeShouldBeOn Verifies that the system.web.customErrors mode is set to On or RemoteOnly. This disable detailed error message returned by ASP.NET to remote users.

MarkVerbHandlersWithValidateAntiforgeryToken Verifies that ValidateAntiforgeryTokenAttribute is used to protect against potential CSRF attacks against ASP.NET MVC applications.

OWASP O2 platform(VisualStudio C# REPL - O2 Platform (v5.1))
The O2 platform represents a new paradigm for how to perform, document and distribute Web Application security reviews. O2 is designed to Automate Application Security Knowledge and Workflows and to Allow non-security experts to access and consume Security Knowledge. We strongly recommend it to .NET developers since this tool helps you identify current security issues in the framework.

O2 Platform is also available as a VisualStudio Extension which you can download from VisualStudio Gallery (see VisualStudio C# REPL - O2 Platform) or directly using VisualStudio's Extension Manager: http://visualstudiogallery.msdn.microsoft.com/295fa0f6-37d1-49a3-b51d-ea4741905dc2

=References= MSDN, 2013, "Declarative Security" available at http://msdn.microsoft.com/en-us/library/kaacwy28.aspx (Last viewed 25th July, 2013) CodePlex, 2010 "Fxcop ASP.NET Security Rules" Available at http://fxcopaspnetsecurity.codeplex.com/ (Last viewed 25th July, 2013)