Last revised: July 17, 2003
Source: CERT/CC
A complete revision history can be found at the end of this file.
Systems Affected
- All Cisco devices running Cisco IOS software and configured to process Internet Protocol version 4 (IPv4) packets
Overview
A vulnerability in many versions of Cisco IOS could allow an intruder to execute a denial-of-service attack against a vulnerable device.I. Description
Cisco IOS is a very widely deployed network operating system. A vulnerability in IOS could allow an intruder to execute a denial-of-service attack against an affected device. Cisco has published an advisory on this topic, available at
http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtmlWe strongly encourage sites using IOS to read this document and take appropriate action.
The CERT/CC is tracking this issue as VU#411332. This reference number corresponds to CVE candidate CAN-2003-0567.
II. Impact
By sending specially crafted IPv4 packets to an interface on a vulnerable device, an intruder can cause the device to stop processing packets destined to that interface. Quoting from Cisco's advisory:
A device receiving these specifically crafted IPv4 packets will force the inbound interface to stop processing traffic. The device may stop processing packets destined to the router, including routing protocol packets and ARP packets. No alarms will be triggered, nor will the router reload to correct itself. This issue can affect all Cisco devices running Cisco IOS software. This vulnerability may be exercised repeatedly resulting in loss of availability until a workaround has been applied or the device has been upgraded to a fixed version of code.
III. Solution
Apply a patch from Cisco
Apply a patch as described in Cisco's Advisory.Restrict access
Until a patch can be applied, you can mitigate the risks presented by this vulnerability by judicious use of access control lists (ACLs). The correct use of ACLs depends on your network topology. Additionally, ACLs may degrade performance on some systems. We recommend reviewing the following before applying ACLs:
http://www.cisco.com/warp/public/707/cisco-sa-20030717-blocked.shtml#workarounds
http://www.cisco.com/warp/public/707/racl.html
http://www.cisco.com/warp/public/707/iacl.html
The CERT Coordination Center thanks Cisco Systems for notifying us about this problem and for helping us to construct this advisory.
Feedback about this advisory may be directed to the author, Shawn Hernan.
Copyright 2003 Carnegie Mellon University.
Revision History
July 16, 2003: Initial release
July 17, 2003: Minor formatting changes