CA2122: Do not indirectly expose methods with link demands

發行項
11/04/2016

Applies to: Visual Studio Visual Studio for Mac

Note

This article applies to Visual Studio 2017. 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
RuleId	CA2122
Category	Microsoft.Security
Breaking change	Non-breaking

Cause

A public or protected member has a Link Demands and is called by a member that does not perform any security checks.

Note

This rule has been deprecated. For more information, see Deprecated rules.

Rule description

A link demand checks the permissions of the immediate caller only. If a member X makes no security demands of its callers, and calls code protected by a link demand, a caller without the necessary permission can use X to access the protected member.

How to fix violations

Add a security Data and Modeling or link demand to the member so that it no longer provides unsecured access to the link demand-protected member.

When to suppress warnings

To safely suppress a warning from this rule, you must make sure that your code does not grant its callers access to operations or resources that can be used in a destructive manner.

Example 1

The following examples show a library that violates the rule, and an application that demonstrates the library's weakness. The sample library provides two methods that together violate the rule. The EnvironmentSetting method is secured by a link demand for unrestricted access to environment variables. The DomainInformation method makes no security demands of its callers before it calls EnvironmentSetting.

using System;
using System.IO;
using System.Security;
using System.Security.Permissions;

namespace SecurityRulesLibrary
{
   public class DoNotIndirectlyExposeMethodsWithLinkDemands
   {
      // Violates rule: DoNotIndirectlyExposeMethodsWithLinkDemands.
      public static string DomainInformation()
      {
         return EnvironmentSetting("USERDNSDOMAIN");
      }

      // Library method with link demand.
      // This method holds its immediate callers responsible for securing the information.
      // Because a caller must have unrestricted permission, the method asserts read permission
      // in case some caller in the stack does not have this permission. 

      [EnvironmentPermissionAttribute(SecurityAction.LinkDemand, Unrestricted=true)]
      public static string EnvironmentSetting(string environmentVariable)
      {
         EnvironmentPermission envPermission = new EnvironmentPermission( EnvironmentPermissionAccess.Read,environmentVariable);
         envPermission.Assert();
  
         return Environment.GetEnvironmentVariable(environmentVariable);
      }
   }
}

Example 2

The following application calls the unsecured library member.

using System;
using SecurityRulesLibrary;
using System.Security;
using System.Security.Permissions;

// You have no permission to access the sensitive information,
// but you will get data from the unprotected method.
[assembly:EnvironmentPermissionAttribute(
   SecurityAction.RequestRefuse,Unrestricted=true)]
namespace TestUnsecuredMembers
{
   class TestUnsecured
   {
      [STAThread]
      static void Main(string[] args)
      {
         string value = null;
         try 
         {
            value = DoNotIndirectlyExposeMethodsWithLinkDemands.DomainInformation();
         }
         catch (SecurityException e) 
         {
            Console.WriteLine(
               "Call to unsecured member was stopped by code access security! {0}",
               e.Message);
            throw;
         }
         if (value != null) 
         {
            Console.WriteLine("Value from unsecured member: {0}", value);
         }
      }
   }
}

This example produces the following output:

*Value from unsecured member: seattle.corp.contoso.com

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