Cisco FWSM SCCP Inspection DoS Vulnerability

A vulnerability exists in the Cisco Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers that may cause the Cisco FWSM to reload after processing a malformed Skinny Client Control Protocol (SCCP) message. The vulnerability exists when SCCP inspection is enabled.

Cisco has released free software updates that address this vulnerability.

All non-fixed 4.x versions of Cisco FWSM Software are affected by this vulnerability if SCCP inspection is enabled. SCCP inspection is enabled by default.

To check if SCCP inspection is enabled, issue the show service-policy | include skinny command and confirm that the command returns output. Example output follows:

fwsm#show service-policy | include skinny
Inspect: skinny , packet 0, drop 0, reset-drop 0

If SCCP inspection is not required, this vulnerability can be mitigated by disabling it. Administrators can disable SCCP inspection by issuing the no inspect skinny command in class configuration sub-mode within the policy map configuration. If SCCP inspection is required, there are no workarounds.

Cisco has released free software updates that address this vulnerability. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

This advisory is posted at

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Calin is a network engineer, with more than 20 years of experience in designing, installing, troubleshooting, and maintaining large enterprise WAN and LAN networks.

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