Vulnerability Note VU#24346

Cisco IOS software vulnerable to DoS via HTTP request containing "%%"

Original Release date: 09 Nov 2000 | Last revised: 30 Mar 2004


There is a denial-of-service vulnerability in several Cisco switch and router products which allows an attacker to force affected devices to crash and reboot.


A vulnerability exists in multiple versions of Cisco's Internetworking Operating System (IOS) software which allows an attacker to force affected switches and routers to crash and reboot. If the IOS HTTP interface is enabled and presented with a request for "http://router-ip/anytext/%%", the software becomes trapped in a loop until a two-minute watchdog timer expires, causing the device to restart.


An attacker can force affected products to reboot, resulting in a denial-of-service while the device is restarting. In some situations, the device may not restart properly without manual intervention such as a power cycle.


Apply a patch from Cisco

Cisco has released an advisory to address this issue and has provided patches for affected versions of the IOS software. For further details, please consult the vendor section of this document.

Disable the HTTP management interface

If it is not possible or practical to immediately patch an affected device, temporarily disabling its HTTP management interface will prevent exploitation of this vulnerability.

Restrict access to the HTTP management interface

If it is not possible to disable the HTTP management interface, users should restrict outside networks from accessing it. For information on how to implement these restrictions, please consult the Cisco advisory at:

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Cisco Systems Inc.Affected-29 Mar 2001
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



The CERT/CC thanks Keith Woodworth for discovering this vulnerability and Cisco for the information contained in their advisory.

This document was written by Jeffrey P. Lanza.

Other Information

  • CVE IDs: CVE-2000-0380
  • Date Public: 26 Apr 2000
  • Date First Published: 09 Nov 2000
  • Date Last Updated: 30 Mar 2004
  • Severity Metric: 11.25
  • Document Revision: 13


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