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Security Activity Bulletin

TCP Split Handshake Connection Security Bypass Vulnerability

 
Threat Type:IntelliShield: Applied Mitigation Bulletin
IntelliShield ID:22462
Version:2
First Published:2011 April 12 18:39 GMT
Last Published:2011 April 14 20:52 GMT
Port: Not available
Urgency:Unlikely Use
Credibility:Confirmed
Severity:Mild Damage
 
Version Summary:

Cisco has released a blog post and released bug reports with additional information to address reports of the TCP split handshake connection vulnerability in Cisco products.

 

Description
 

Researchers from NSS Labs have announced that the Cisco ASA Adaptive Security Appliance (along with products from other firewall vendors) is affected by the TCP Split Handshake weakness initially discovered by BreakingPoint Systems.  Cisco engineers have been unable to confirm the vulnerability in any Cisco products.

The weakness could allow an attacker to establish connections through targeted devices even where connections may otherwise be disabled in access control lists (ACLs) or filter rules.  TCP connections using a split handshake to establish a session could also bypass filtering for malicious activity because filtering devices may be unable to detect communications within connections established out of the norm.

As a matter of policy, Cisco takes security vulnerabilities very seriously and we continue to take active measures to safeguard the security and reliability of our equipment. Cisco has been working with NSS Labs on the TCP split handshake spoof since early this year. In this time, Cisco PSIRT has been unable to confirm any new security vulnerabilities in Cisco products, and have demonstrated the Cisco ASA protects against this attack.  Cisco PSIRT continues to work with NSS Labs, and will follow our well-established disclosure process should any new information come to light.  PSIRT will disclose any security vulnerabilities discovered in compliance with the Cisco security vulnerability policy: Cisco Security Vulnerability Policy 

Cisco has released a blog post regarding the investigation into reported vulnerabilities in Cisco products at the following link: Cisco Investigation for TCP Split-Handshake Issue Reported by NSS

Cisco has released the following bug reports for registered customers:

 

 
Alert History
 
Version 1, April 12, 2011, 2:39 PM: Multiple vendor firewall devices may contain a weakness that could allow attackers to evade filtering or bypass security restrictions.


Product Sets
 
The security vulnerability applies to the following combinations of products.

Primary Products:
IntelliShieldSecurity Activity Bulletin Original Release Base

Associated Products:
N/A




Alerts and bulletins on the Cisco Security Intelligence Operations Portal are highlighted by analysts in the Cisco Threat Operations Center and represent a subset of the comprehensive content that is available through Cisco Security IntelliShield Alert Manager Service. This customizable threat and vulnerability alert service provides security staff with access to timely, accurate, and credible information about threats and vulnerabilities that may affect their environment.


LEGAL DISCLAIMER
The urgency and severity ratings of this alert are not tailored to individual users; users may value alerts differently based upon their network configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.
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