Cisco Security Advisory

Advisory ID: cisco-sa-20051201-http

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051201-http

Revision 2.0

For Public Release 2005 December 1 21:00  UTC (GMT)

Summary

A vulnerability exists in the IOS HTTP server in which HTML code inserted into dynamically generated output, such as the output from a show buffers command, will be passed to the browser requesting the page. This HTML code could be interpreted by the client browser and potentially execute malicious commands against the device or other possible cross-site scripting attacks. Successful exploitation of this vulnerability requires that a user browse a page containing dynamic content in which HTML commands have been injected.

Cisco will be making free software available to address this vulnerability for affected customers. There are workarounds available to mitigate the effects of the vulnerability.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051201-http.

Affected Products

The Cisco IOS Web browser interface (which enables the device to perform as an HTTP server) allows configuration and monitoring of a router or access server using any web browser. This feature was introduced in IOS 11.0.

A vulnerability exists in the IOS HTTP server in which HTML code inserted into dynamically generated output, such as the output from a show buffers command, will be passed to the browser requesting the page. This HTML code could be interpreted by the browser and potentially execute malicious commands against the device or other possible cross-site scripting attacks.

In order to be vulnerable to the cross-site scripting attack, a user must browse and view the content during the same period of time the injected code exists in memory. On the other hand, if a user does not browse contaminated dynamic content on the device, then exploitation is not possible.

A proof of concept exploit exists for this vulnerability, in which the exploit attempts to reset the enable password on the device. For the attack to work against the device itself, the user browsing tainted dynamic content on the router will only be able to execute commands at or below the privilege level for which they are authenticated and authorized for on the device.

This vulnerability is documented in Cisco Bug ID CSCsc64976 ( registered customers only) .

Successful exploitation of the vulnerability may result in an attacker executing commands on the device, including the possibility of gaining full administrative privileges on the device which is dependent on the privilege level of the authenticated user.

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.

Each row of the Cisco IOS software table (below) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. Cisco recommends upgrading to the latest available release where possible.

If the HTTP server is not used for any legitimate purposes on the device, it is a best practice to disable it by issuing the following commands in configure mode:

no ip http server
no ip http secure-server

Disable the HTTP WEB_EXEC Service

A feature was introduced in 12.3(14)T and later in which selective HTTP and HTTPS services could be enabled or disabled. The WEB_EXEC service provides a facility to configure the box and retrieve the current state of the box from remote clients.

It is possible to disable the WEB_EXEC service while still leaving other HTTP services active. If an installation does not require the use of the WEB_EXEC service, then it may be disabled using the following procedure:

1. Verify the list of all session modules.
   

   Router#show ip http server session-module 
   HTTP server application session modules: 
    Session module Name  Handle Status   Secure-status  Description 
   HTTP_IFS              1      Active   Active         HTTP based IOS File Server 
   HOME_PAGE             2      Active   Active         IOS Homepage Server 
   QDM                   3      Active   Active         QOS Device Manager Server 
   QDM_SA                4      Active   Active         QOS Device Manager Signed Applet Server 
   WEB_EXEC              5      Active   Active         HTTP based IOS EXEC Server 
   IXI                   6      Active   Active         IOS XML Infra Application Server 
   IDCONF                7      Active   Active         IDCONF HTTP(S) Server 
   XSM                   8      Active   Active         XML Session Manager 
   VDM                   9      Active   Active         VPN Device Manager Server 
   XML_Api               10     Active   Active         XML Api 
   ITS                   11     Active   Active         IOS Telephony Service 
   ITS_LOCDIR            12     Active   Active         ITS Local Directory Search 
   CME_SERVICE_URL       13     Active   Active         CME Service URL 
   CME_AUTH_SRV_LOGIN    14     Active   Active         CME Authentication Server 
   IPS_SDEE              15     Active   Active         IOS IPS SDEE Server 
   tti-petitioner        16     Active   Active         TTI Petitioner

2. Create a list of session modules that are required, in this example it would be everything other than WEB_EXEC.
   

   Router#configuration terminal
   Router(config)#ip http session-module-list exclude_webexec 
                HTTP_IFS,HOME_PAGE,QDM,QDM_SA,IXI,IDCONF,XSM,VDM,XML_Api,
                ITS,ITS_LOCDIR,CME_SERVICE_URL,CME_AUTH_SRV_LOGIN,IPS_SDEE,tti-petitioner
   

3. Selectively enable HTTP/HTTPS applications that will service incoming HTTP requests from remote clients.
   

   Router(config)#ip http active-session-modules exclude_webexec 
   Router(config)#ip http secure-active-session-modules exclude_webexec 
   Router(config)#exit 
   

4. Verify the list of all session modules, and ensure WEB_EXEC is not active.
   

   Router#show ip http server session-module 
   HTTP server application session modules: 
    Session module Name  Handle Status   Secure-status  Description 
   HTTP_IFS              1      Active   Active         HTTP based IOS File Server 
   HOME_PAGE             2      Active   Active         IOS Homepage Server 
   QDM                   3      Active   Active         QOS Device Manager Server 
   QDM_SA                4      Active   Active         QOS Device Manager Signed Applet Server 
   WEB_EXEC              5      Inactive Inactive       HTTP based IOS EXEC Server 
   IXI                   6      Active   Active         IOS XML Infra Application Server 
   IDCONF                7      Active   Active         IDCONF HTTP(S) Server 
   XSM                   8      Active   Active         XML Session Manager 
   VDM                   9      Active   Active         VPN Device Manager Server 
   XML_Api               10     Active   Active         XML Api 
   ITS                   11     Active   Active         IOS Telephony Service 
   ITS_LOCDIR            12     Active   Active         ITS Local Directory Search 
   CME_SERVICE_URL       13     Active   Active         CME Service URL 
   CME_AUTH_SRV_LOGIN    14     Active   Active         CME Authentication Server 
   IPS_SDEE              15     Active   Active         IOS IPS SDEE Server 
   tti-petitioner        16     Active   Active         TTI Petitioner 

For further information on selective enabling of applications using an HTTP or secure HTTP server, consult the Cisco IOS network management configuration guide, release 12.4T at: http://www.cisco.com/en/US/docs/ios/netmgmt/configuration/guide/nm_http_app_enable.html

Avoid the use of Web-based SHOW commands

Successful exploitation of this vulnerability requires an unsuspecting user to request dynamic content from the device via the "show" commands which are available. Avoiding the use of those commands via the web interface until an upgrade to fixed software is possible may be perfectly legitimate for some installations.

Cisco will make free software available to address this vulnerability for affected customers. This advisory will be updated as fixed software becomes available. 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.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades.

Customers with Service Contracts

Customers Using Third-Party Support Organizations

Customers Without Service Contracts

This vulnerability was disclosed in a public posting to the Bugtraq mailing list.

We would like to thank iDefense for finding and initially reporting this vulnerability to us.

We would also like to thank Mr. Adrian Pastor from ProCheckup Ltd for sharing information with us about another possible vector into this vulnerability. His research paper is available at http://www.procheckup.com/vulnerability_manager/vulnerabilities/paper-04 .

The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory.

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.

This advisory is posted on Cisco's worldwide website at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20051201-http.

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

• cust-security-announce@cisco.com
  
• first-teams@first.org
  
• bugtraq@securityfocus.com
  
• vulnwatch@vulnwatch.org
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• full-disclosure@lists.grok.org.uk
  
• comp.dcom.sys.cisco@newsgate.cisco.com
  

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt/.