CERT Advisory CA-2001-14 Cisco IOS HTTP Server Authentication Vulnerability

   Original release date: June 28, 2001
   Last revised: --
   Source: CERT/CC
   
   A complete revision history can be found at the end of this file.
   
Systems Affected

     * Cisco IOS systems using local authentication databases with the
       HTTP server enabled
       
Overview

   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.
   
I. Description

   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:
   
          http://<address>/level/XX/exec/...
          
   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:
   
          http://www.cisco.com/warp/public/707/IOS-httplevel-pub.html
          
II. Impact

   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.
   
III. Solution

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:
   
          http://www.cisco.com/warp/public/480/tacplus.shtml
          
Appendix A. - Vendor Information

   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 Systems

   Cisco has published a security advisory describing this vulnerability
   at
   
          http://www.cisco.com/warp/public/707/IOS-httplevel-pub.html
     _________________________________________________________________
   
   The CERT/CC thanks Cisco Systems for their advisory, on which this
   document is based.
     _________________________________________________________________
   
   Author: Cory F. Cohen
   ______________________________________________________________________
   
   This document is available from:
   http://www.cert.org/advisories/CA-2001-14.html
   ______________________________________________________________________
   
CERT/CC Contact Information

   Email: cert@cert.org
          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
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          Carnegie Mellon University
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          U.S.A.
          
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   Revision History
June 28, 2001:  Initial release