Visual Studio Team System
Do not indirectly expose methods with link demands

TypeName

DoNotIndirectlyExposeMethodsWithLinkDemands

CheckId

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.

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 Access 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

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.

C# 
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);
      }
   }
}

The following application calls the unsecured library member.

C# 
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
See Also

Concepts

Link Demands

Other Resources

Secure Coding Guidelines
Data Access
Tags :


Community Content

csnyderasdfasdf
VB.Net Code
 Example 


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. 
 
Imports System 
Imports System.IO 
Imports System.Security 
Imports System.Security.Permissions 
Namespace SecurityRulesLibrary 
    Public Class DoNotIndirectlyExposeMethodsWithLinkDemands 
        ' Violates rule: DoNotIndirectlyExposeMethodsWithLinkDemands. 
        Public Shared Function DomainInformation() As String 
            Return EnvironmentSetting("USERDNSDOMAIN") 
        End Function 

        ' 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 Shared Function EnvironmentSetting(ByVal environmentVariable As String) As String 
            Dim envPermission As New EnvironmentPermission(EnvironmentPermissionAccess.Read, environmentVariable) 
            envPermission.Assert() 

            Return Environment.GetEnvironmentVariable(environmentVariable) 
        End Function 
    End Class 
End Namespace

Tags : code vb.net

csnyderasdfasdf
The following application calls the unsecured library member.
Imports System 
Imports System.IO 
Imports System.Security 
Imports System 
Imports SecurityRulesLibrary 
Imports System.Security 
Imports 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()> _ 
        Private Shared Sub Main(ByVal args As String()) 
            Dim value As String = Nothing 
            Try 
                value = DoNotIndirectlyExposeMethodsWithLinkDemands.DomainInformation() 
            Catch e As SecurityException 
                Console.WriteLine("Call to unsecured member was stopped by code access security! {0}", e.Message) 
                Throw 
            End Try 
            If value IsNot Nothing Then 
                Console.WriteLine("Value from unsecured member: {0}", value) 
            End If 
        End Sub 
    End Class 
End Namespace
Tags :

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