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Cisco Security Advisory: TFTP Long Filename Vulnerability


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Date: Tue, 30 Jul 2002 12:00:00 -0400
From: Cisco Systems Product Security Incident Response Team <psirt@cisco.com.>
To: [email protected]
Subject: Cisco Security Advisory: TFTP Long Filename Vulnerability
Cc: [email protected]

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Cisco Security Advisory: TFTP Long Filename Vulnerability

Revision 1.0: Final For Public Release 2002 July 30 18:00 GMT - ------------------------------------------------------------------------------- Contents ======== Summary Affected Products Details Impact Software Versions and Fixes Obtaining Fixed Software Workarounds Exploitation and Public Announcements Status of This Notice Distribution Revision History Cisco Security Procedures - ------------------------------------------------------------------------------- Summary ======= Trivial File Transfer Protocol (TFTP) is a protocol which allows for easy transfer of files between network connected devices. A vulnerability has been discovered in the processing of filenames within a TFTP read request when Cisco IOS is configured to act as a TFTP server. The following products are identified as affected by this vulnerability: * Cisco IOS software versions 11.1, 11.2, 11.3 Unless explicitly stated otherwise, all other Cisco products are not affected. A simple workaround exists for this vulnerability which is detailed in the Workarounds section below. This advisory is available at http://www.cisco.com/warp/public/707/ios-tftp-long-filename-pub.shtml. Affected Products ================= The following products are affected: * Cisco IOS software versions 11.1, 11.2, 11.3 The following products are not affected: * Cisco IOS software versions 11.1, 11.2, 11.3 when running on a 68040 based architecture such as a Route Processor. Only this specific architecture is not vulnerable to a reload with the above generally affected versions. Other devices such as Route Switch Processors are affected. To verify which type of route processor you have, issue the command "show version" at the prompt on the router and look for a string similar to: cisco RP1 (68040) processor (revision A0) with 16384K bytes of memory. * Cisco IOS software versions 12.0 and up. Details ======= By sending a crafted TFTP read request it is possible to trigger a buffer overflow in the TFTP server when no alias for all files being served have been defined. This vulnerability can be exploited remotely. The successful exploitation may cause a software reset of the device. This vulnerability has been documented as CSCdy03429. Impact ====== Successful exploitation of this vulnerability may cause a software reset of the device resulting in a loss of availability while the device reinitializes. Repeated exploitations could result in a Denial of Service until the workarounds for this vulnerability have been implemented. Software Versions and Fixes
The affected releases, 11.1, 11.2, and 11.3, are all at End of Life, which means they do not have a maintenance version scheduled, and will not be fixed. It is recommended to use the documented workarounds if these versions must be used. Obtaining Fixed Software
As the affected versions are not scheduled to be fixed, and a simple workaround is available, a software upgrade is not required to address this vulnerability. However, if you have a service contract, and wish to upgrade to unaffected code, you may obtain upgraded software through your regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's Worldwide Web site at http://www.cisco.com. If you need assistance with the implementation of the workarounds, or have questions on the workarounds, please contact the Cisco Technical Assistance Center (TAC). Cisco TAC contacts are as follows: * +1 800 553 2447 (toll free from within North America) * +1 408 526 7209 (toll call from anywhere in the world) * e-mail: [email protected] See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages. Please do not contact either "[email protected]" or "[email protected]" for software upgrades. Workarounds =========== There are two workarounds known to address this issue. Disable the TFTP server entirely Cisco IOS provides TFTP server functionality to facilitate the transfer of Cisco IOS images when another TFTP server may not be available. If the TFTP server functionality is not currently needed, the following steps may be taken to disable the TFTP server. 1. While in enable mode on the router, issue the command "show running-config" and look for lines starting with "tftp-server". 2. For each line in the config starting with "tftp-server", prepend the word "no" followed by a space followed by the full text of the matching line in config mode to remove that entry. This step must be repeated for each matching line of the config. 3. Once this task has been completed, verify that there are no lines starting with "tftp-server" by issuing the command "show running-config" from the enable prompt. 4. Once verified, save the new configuration so that the server will be disabled upon the next reset of the device. Provide aliases for TFTP server filenames Cisco IOS provides the ability to alias a long filename to a shorter filename. If the tftp-server entries in the configuration have the keyword "alias" in them, the router will not be vulnerable to exploitation of this vulnerability. To implement this workaround, follow the directions above for disabling the TFTP server, and then add any configuration lines back to the config by appending the keyword "alias" followed by a short filename such that the command resembles: tftp-server flash rsp-jv-mz.111-24a alias CiscoIOS Note that this must be done for every line starting with "tftp-server" in the configuration. The existence of a single line in the configuration beginning with "tftp-server" without an alias defined while running affected versions of software is all that is needed to become subject to this vulnerability. Exploitation and Public Announcements
This vulnerability was announced on the BUGTRAQ mailing list on 2002-07-27 (http://online.securityfocus.com/archive/1/284634). The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory. Status of This Notice: FINAL
This is a final notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this notice unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this notice. Distribution ============ This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/ios-tftp-long-filename-pub.shtml. 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: * [email protected] * [email protected] * [email protected] (includes CERT/CC) * [email protected] * [email protected] * comp.dcom.sys.cisco * [email protected] * Various internal Cisco mailing lists Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History ================ +-------------------------------------------------------------------------+ |Revision Number 1.0 |2002-July-30 18:00 |Initial Public Release | | |GMT | | +-------------------------------------------------------------------------+ Cisco Security Procedures
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 Web site at http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco security notices. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt/. - ------------------------------------------------------------------------------- This notice is Copyright 2002 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, and include all date and version information. - ------------------------------------------------------------------------------- -----BEGIN PGP SIGNATURE----- Version: PGP 6.5.2 iQA/AwUBPUa0t5PS/wbyNnWcEQKmggCgyFDCj3UxBpdsFOChfdx0Iy4pbicAoI4V uvYuWIRCisFjDIx4SIaeSG9r =SrnK -----END PGP SIGNATURE-----

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