Cisco IOS HTTP Server Authentication Vulnerability
Last revised: --
A complete revision history can be found at the end of this file.
- Cisco IOS systems using local authentication databases with the HTTP server enabled
A problem with the HTTP server component of Cisco IOS system software allows an intruder to execute privileged commands on Cisco routers if local authentication databases are used.
By sending a particular URL to a Cisco IOS device with the HTTP server enabled, a remote attacker may be able to execute commands at the highest privilege level (15). The malicious URL is of the following form:
The value of XX is a number between 16 and 99. While a single malicious URL will not work consistently against all devices, the limited number of possible URLs can allow an attacker to try each URL until the attack succeeds.
This problem occurs if the system is using a local authentication database, but not if the Terminal Access Controller Access Control System (TACACS+) or Radius authentication systems are used.
Cisco has published a security advisory describing this vulnerability and its solutions, in more detail at:
A remote attacker can execute arbitrary commands at the highest privilege level (15) on systems using local authentication databases with the HTTP server enabled. This access allows a remote attacker to inspect or change the configuration of the device, effectively allowing complete control.
Upgrade your IOS Release
Cisco has published detailed information about upgrading affected Cisco IOS software to correct this vulnerability. System managers are encouraged to upgrade to one of the non-vulnerable releases.
Disable the HTTP server
Because this problem exists in the handling of HTTP requests, disabling the HTTP server prevents the vulnerability from being exploited. Information about disabling the HTTP server is provided in the Cisco security advisory on this topic.
Enable TACACS+ or Radius Authentication
This vulnerability is not present when the Terminal Access Controller Access Control System (TACACS+) or Radius authentication systems are used. Enabling one of these authentication mechanisms in place of local authorization databases will prevent the vulnerability from being exploited. Information about enabling TACACS+ or Radius can be found in the following Cisco document:
This appendix contains information provided by vendors for this advisory. When vendors report new information to the CERT/CC, we update this section and note the changes in our revision history. If a particular vendor is not listed below, we have not received their comments.
Cisco has published a security advisory describing this vulnerability at
The CERT/CC thanks Cisco Systems for their advisory, on which this document is based.
Author: Cory F. Cohen
Copyright 2001 Carnegie Mellon University.
June 28, 2001: Initial release