Cisco has reported  (at
http://www.cisco.com/warp....b.shtml   ) a
problem in the Cisco PIX Firewall AAA authentication system which could
allow a denial of service attack. This vulnerability does not affect the IOS
Firewall feature set or any other Cisco products.

When AAA authentication services are configured on the Cisco Secure PIX
Firewall the problem could allow an attacker to consume all authentication
system resources. The denial of service would only affect these resources -
therefore blocking new requests -, other functions would continue to operate
normally.

This bug affects users of Cisco Secure PIX Firewalls with software versions
4.0 up to and including 4.4(8), 5.0(3), 5.1(3), 5.2(2), and 5.3(1) with
configurations using AAA authentication.

The affected configurations have configuration lines that begin:

pixfirewall#  aaa authentication ...

Configurations without "aaa authentication" are not affected, nor are
versions 6.0 and later of PIX Firewall.