CA2124: Wrap vulnerable finally clauses in outer try

Article
11/15/2016

Note

This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

Item	Value
TypeName	WrapVulnerableFinallyClausesInOuterTry
CheckId	CA2124
Category	Microsoft.Security
Breaking Change	Non Breaking

Cause

In versions 1.0 and 1.1 of the .NET Framework, a public or protected method contains a try/catch/finally block. The finally block appears to reset security state and is not enclosed in a finally block.

Rule Description

This rule locates try/finally blocks in code that targets versions 1.0 and 1.1 of the .NET Framework that might be vulnerable to malicious exception filters present in the call stack. If sensitive operations such as impersonation occur in the try block, and an exception is thrown, the filter can execute before the finally block. For the impersonation example, this means that the filter would execute as the impersonated user. Filters are currently implementable only in Visual Basic.

Warning

In versions 2.0 and later of the .NET Framework, the runtime automatically protects a try/catch/ finally block from malicious exception filters, if the reset occurs directly within the method that contains the exception block.

How to Fix Violations

Place the unwrapped try/finally in an outer try block. See the second example that follows. This forces the finally to execute before filter code.

When to Suppress Warnings

Do not suppress a warning from this rule.

Pseudo-code Example

Description

The following pseudo-code illustrates the pattern detected by this rule.

Code

try {
   // Do some work.
   Impersonator imp = new Impersonator("John Doe");
   imp.AddToCreditCardBalance(100);
}
finally {
   // Reset security state.
   imp.Revert();
}

Example

The following pseudo-code shows the pattern that you can use to protect your code and satisfy this rule.

try {
     try {
        // Do some work.
     }
     finally {
        // Reset security state.
     }
}
catch()
{
    throw;
}

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