Cisco IOS Vulnerability

Cisco IOS Interface Blocked by IPv4 Packets

A nasty vulnerability has been discovered that could affect most of the Cisco routers in NZ. It allows a remote user to stop a router from processing packets. You can read the official Cisco notice on Cisco's WWW site.

Devices NOT affected:

• Any router running a config from this WWW site that says it is a firewall config.
• Any router running IOS V12.3 or better (12.2(13)ZH2 for the 837 also has the fix).
• Any PIX box.

If you want to obtain a "fixed" version of the IOS software for your router you can do this free of charge by sending an email to tac@cisco.com, including the serial number of your Cisco device, the output of "show ver" (which normally includes the serial number), and a link to the official Cisco notice about the vulnerability (listed above).

If you just want to protect your router against attack, then you can either use one of the firewall config's from this WWW site, or add an access-list like the one below to stop traffic coming in on the interface that connects your router to the Internet.