Cisco Secure PIX Firewall Forged TCP RST Vulnerability

A connection through a Cisco Secure PIX Firewall can be reset by a third party if the source and destination IP addresses and ports of the connection can be determined or inferred. This can be accomplished by sending a forged TCP Reset (RST) packet to the firewall, containing the same source and destination addresses and ports (in the TCP packet header) as the connection to be disrupted. The attacker would have to possess detailed knowledge of the connection table in the firewall (which is used to track outgoing connections and disallow any connections from the external network that were not initiated by an internal machine) or be able to otherwise determine the required IP address and port information to exploit this.


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