Asterisk Project Security Advisory - AST-2019-003

         Product        Asterisk                                              
         Summary        Remote Crash Vulnerability in chan_sip channel        
    Nature of Advisory  Denial of Service                                     
      Susceptibility    Remote Unauthenticated Sessions                       
         Severity       Minor                                                 
      Exploits Known    No                                                    
       Reported On      June 28, 2019                                         
       Reported By      Francesco Castellano                                  
        Posted On       July 1, 2019                                          
     Last Updated On    July 2, 2019                                          
     Advisory Contact   Jcolp AT sangoma DOT com                              
         CVE Name       CVE-2019-13161                                        

    Description  When T.38 faxing is done in Asterisk a T.38 reinvite may be  
                 sent to an endpoint to switch it to T.38. If the endpoint    
                 responds with an improperly formatted SDP answer including   
                 both a T.38 UDPTL stream and an audio or video stream        
                 containing only codecs not allowed on the SIP peer or user   
                 a crash will occur. The code incorrectly assumes that there  
                 will be at least one common codec when T.38 is also in the   
                 SDP answer.                                                  
                 This requires Asterisk to initiate a T.38 reinvite which is  
                 only done when executing the ReceiveFax dialplan             
                 application or performing T.38 passthrough where a remote    
                 endpoint has requested T.38.                                 
                 For versions of Asterisk 13 before 13.21.0 and Asterisk 15   
                 before 15.4.0 the “preferred_codec_only” option must also  
                 be set to “yes”. If set to “no” the crash will not 

    Resolution  If T.38 faxing is not required this functionality can be      
                disabled by ensuring the “t38pt_udptl” is set to “no” 
so a    
                T.38 reinvite is not possible.                                
                If T.38 faxing is required then Asterisk should be upgraded   
                to a fixed version. The problem can also be limited in scope  
                by enabling T.38 faxing only for endpoints which actually     
                participate in fax.                                           

                               Affected Versions
                Product              Release Series  
         Asterisk Open Source             13.x       All releases             
         Asterisk Open Source             15.x       All releases             
         Asterisk Open Source             16.x       All releases             
          Certified Asterisk             13.21       All releases             

                                  Corrected In
                    Product                              Release              
              Asterisk Open Source                       13.27.1              
              Asterisk Open Source                        15.7.3              
              Asterisk Open Source                        16.4.1              
               Certified Asterisk                      13.21-cert4            

                                SVN URL                               Revision    Asterisk  
                                                                      13      Asterisk  
                                                                      15      Asterisk  
                                                                      16   Certified 


    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         
    July 1, 2019       Joshua Colp              Initial revision              

               Asterisk Project Security Advisory - AST-2019-003
               Copyright © 2019 Digium, Inc. All Rights Reserved.
  Permission is hereby granted to distribute and publish this advisory in its
                           original, unaltered form.

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