Re: Cisco Phone 7940 remote DOS

[Clay Seaman-Kossmey <ckossmey () cisco com>]

Hello -

This is Cisco's response to the message posted by Radu State to full- 
disclosure on Wednesday Dec 5 2007.  Cisco greatly appreciates the  
opportunity to work with researchers on security vulnerabilities, and  
welcomes the opportunity to review and assist in product reports.

Cisco confirms that there is an issue whereby a crafted sequence of  
SIP messages may cause the phone to enter a state where no calls can  
be placed from, or received by a Cisco IP phone running Session  
Initiation Protocol (SIP) software.  Once the crafted SIP messages  
stop, the device will return to normal service.  This issue is  
tracked by Cisco bug ID CSCsl63427.  Registered customers will be  
able to view additional information here

http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do? 
method=fetchBugDetails&bugId=CSCsl63427

This issue is not seen when the SIP phone is registered to a Cisco  
Unified Communications Manager (CUCM) server, as additional checking  
is done that would prevent the attack.

Cisco was unable to reproduce the device restart as described by Mr.  
State.

This issue has been assigned the Common Vulnerabilities and Exposures  
identifier of CVE-2007-5583.

As a possible mitigation for this issue, Cisco recommends, as a best  
practice, that voice infrastructure devices are kept on separate
networks from data devices.  In this case, the crafted packets may be  
prevented from reaching the
voice devices.

Regards,

Clay Seaman-Kossmeyer
Cisco PSIRT

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