Vulnerability Note VU#291924
Multiple Telnet clients fail to properly handle the "LINEMODE" SLC suboption
Multiple Telnet clients contain a data length validation flaw which may allow a server to induce arbitrary code execution on the client host.
The Telnet network protocol is described in RFC854 and RFC855 as a general, bi-directional communications facility. The Telnet protocol is commonly used for command line login sessions between Internet hosts.
Many Telnet client implementations may be vulnerable to a flaw which may allow arbitrary code to be executed on the connected client. The Telnet server may supply a specially crafted reply containing a larger number of RFC1184 LINEMODE "Set Local Character" (SLC) suboption commands, which are not checked for proper length before being stored into a fixed length buffer. Affected Telnet clients possibly include the BSD Telnet implementation and the MIT Kerberos distribution.
The Telnet LINEMODE mode is enabled by default in a majority of modern Telnet clients and servers, and is often negotiated automatically before user input is required. Therefore, an attacker may be able to launch a vulnerable client, for example, through commands embedded in web pages such as an IFRAME with a "telnet:" URL, and exploit this flaw requiring only minimal or no user interaction.
A remote server may be able to execute arbitrary code under the permissions of the user running the Telnet client on the local host.
Apply an update from your vendor
Patches, updates, and fixes are available from multiple vendors.
As a workaround, the client may explicitly disable the LINEMODE mode before connecting in order to prevent LINEMODE command processing. In addition, as a best practice clients should never connect to unknown servers.
If you are a vendor and your product is affected, let
us know.View More »
|Vendor||Status||Date Notified||Date Updated|
|Apple Computer, Inc.||Affected||28 Mar 2005||01 Apr 2005|
|Debian Linux||Affected||28 Mar 2005||29 Mar 2005|
|F5 Networks, Inc.||Affected||28 Mar 2005||02 May 2005|
|Mandriva, Inc.||Affected||28 Mar 2005||01 Apr 2005|
|MiT Kerberos Development Team||Affected||-||29 Mar 2005|
|Red Hat, Inc.||Affected||28 Mar 2005||22 Dec 2005|
|Sun Microsystems, Inc.||Affected||28 Mar 2005||29 Mar 2005|
|Microsoft Corporation||Not Affected||28 Mar 2005||01 Apr 2005|
|Cray Inc.||Unknown||28 Mar 2005||29 Mar 2005|
|EMC Corporation||Unknown||28 Mar 2005||29 Mar 2005|
|Engarde||Unknown||28 Mar 2005||29 Mar 2005|
|FreeBSD, Inc.||Unknown||28 Mar 2005||29 Mar 2005|
|Fujitsu||Unknown||28 Mar 2005||29 Mar 2005|
|Hitachi||Unknown||28 Mar 2005||29 Mar 2005|
|HP||Unknown||28 Mar 2005||29 Mar 2005|
Thanks to iDEFENSE Labs for reporting this vulnerability.
This document was written by Ken MacInnis.
28 Mar 2005
Date First Published:
29 Mar 2005
Date Last Updated:
22 Dec 2005
If you have feedback, comments, or additional information about this vulnerability, please send us email.