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: