Cisco Cisco IOS Software Release 12.4(2)XB6

Media Gateway Control Protocol (MGCP) 

Signaling protocols H.323, H.254 

Real-time Transport Protocol (RTP) 

Facsimile reception 

Cisco has made free software available to address these vulnerabilities for affected customers. Fixed 
Cisco IOS software listed in the Software Versions and Fixes section contains fixes for all 
vulnerabilities mentioned in this advisory.

There are no workarounds available to mitigate the effects of any of the vulnerabilities apart from 
disabling the protocol or feature itself. 

This advisory is posted at 

There are no open caveats in this release. 

There are no resolved caveats in this release. 

There are no open caveats in this release. 

CSCsd85587

A vulnerability has been discovered in a third party cryptographic library which is used by a number 
of Cisco products. This vulnerability may be triggered when a malformed Abstract Syntax Notation 
One (ASN.1) object is parsed. Due to the nature of the vulnerability it may be possible, in some 
cases, to trigger this vulnerability without a valid certificate or valid application-layer credentials 
(such as a valid username or password).

Successful repeated exploitation of any of these vulnerabilities may lead to a sustained 
Denial-of-Service (DoS); however, vulnerabilities are not known to compromise either the 
confidentiality or integrity of the data or the device. These vulnerabilities are not believed to allow 
an attacker will not be able to decrypt any previously encrypted information.

The vulnerable cryptographic library is used in the following Cisco products:

Cisco IOS, documented as Cisco bug ID CSCsd85587 

Cisco IOS XR, documented as Cisco bug ID CSCsg41084 

Cisco PIX and ASA Security Appliances, documented as Cisco bug ID CSCse91999 

Cisco Unified CallManager, documented as Cisco bug ID CSCsg44348