AST-2012-012: Asterisk Manager User Unauthorized Shell Access

From: Asterisk Security Team <>
Subject: AST-2012-012: Asterisk Manager User Unauthorized Shell Access

               Asterisk Project Security Advisory - AST-2012-012

          Product         Asterisk                                            
          Summary         Asterisk Manager User Unauthorized Shell Access     
     Nature of Advisory   Permission Escalation                               
       Susceptibility     Remote Authenticated Sessions                       
          Severity        Minor                                               
       Exploits Known     No                                                  
        Reported On       July 13, 2012                                       
        Reported By       Zubair Ashraf of IBM X-Force Research               
         Posted On        August 30, 2012                                     
      Last Updated On     August 30, 2012                                     
      Advisory Contact    Matt Jordan < mjordan AT digium DOT com >           
          CVE Name        CVE-2012-2186                                       

    Description  The AMI Originate action can allow a remote user to specify  
                 information that can be used to execute shell commands on    
                 the system hosting Asterisk. This can result in an unwanted  
                 escalation of permissions, as the Originate action, which    
                 requires the "originate" class authorization, can be used    
                 to perform actions that would typically require the          
                 "system" class authorization. Previous attempts to prevent   
                 this permission escalation (AST-2011-006, AST-2012-004)      
                 have sought to do so by inspecting the names of              
                 applications and functions passed in with the Originate      
                 action and, if those applications/functions matched a        
                 predefined set of values, rejecting the command if the user  
                 lacked the "system" class authorization. As reported by IBM  
                 X-Force Research, the "ExternalIVR" application is not       
                 listed in the predefined set of values. The solution for     
                 this particular vulnerability is to include the              
                 "ExternalIVR" application in the set of defined              
                 applications/functions that require "system" class           
                 Unfortunately, the approach of inspecting fields in the      
                 Originate action against known applications/functions has a  
                 significant flaw. The predefined set of values can be        
                 bypassed by creative use of the Originate action or by       
                 certain dialplan configurations, which is beyond the         
                 ability of Asterisk to analyze at run-time. Attempting to    
                 work around these scenarios would result in severely         
                 restricting the applications or functions and prevent their  
                 usage for legitimate means. As such, any additional          
                 security vulnerabilities, where an application/function      
                 that would normally require the "system" class               
                 authorization can be executed by users with the "originate"  
                 class authorization, will not be addressed. Instead, the     
                 README-SERIOUSLY.bestpractices.txt file has been updated to  
                 reflect that the AMI Originate action can result in          
                 commands requiring the "system" class authorization to be    
                 executed. Proper system configuration can limit the impact   
                 of such scenarios.                                           
                 The next release of each version of Asterisk will contain,   
                 in addition to the fix for the "ExternalIVR" application,    
                 an updated README-SERIOUSLY.bestpractices.txt file.          

    Resolution  Asterisk now checks for the "ExternalIVR" application when    
                processing the Originate action.                              
                Additionally, the README-SERIOUSLY.bestpractices.txt file     
                has been updated. It is highly recommended that, if AMI is    
                utilized with accounts that have the "originate" class        
                authorization, Asterisk is run under a defined user that      
                does not have root permissions. Accounts with the             
                "originate" class authorization should be treated in a        
                similar manner to those with the "system" class               

                               Affected Versions
               Product                 Release Series       
        Asterisk Open Source                1.8.x           All versions      
        Asterisk Open Source                10.x            All versions      
         Certified Asterisk                1.8.11           All versions      
        Asterisk Digiumphones        10.x.x-digiumphones    All versions      
      Asterisk Business Edition             C.3.x           All versions      

                                  Corrected In
                   Product                              Release               
             Asterisk Open Source         , 10.7.1          
              Certified Asterisk                      1.8.11-cert6            
            Asterisk Digiumphones                 10.7.1-digiumphones         
          Asterisk Business Edition                     C.3.7.6               

                               SVN URL                              Revision Asterisk  
                                                                       1.8   Asterisk  


    Asterisk Project Security Advisories are posted at                                                             
    This document may be superseded by later versions; if so, the latest      
    version will be posted at                                             and                        

                                Revision History
          Date                  Editor                 Revisions Made         
    08/27/2012         Matt Jordan               Initial version              

               Asterisk Project Security Advisory - AST-2012-012
              Copyright (c) 2012 Digium, Inc. All Rights Reserved.
  Permission is hereby granted to distribute and publish this advisory in its
                           original, unaltered form.

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