Vulnerability Note VU#291924

Multiple Telnet clients fail to properly handle the "LINEMODE" SLC suboption

Original Release date: 29 Mar 2005 | Last revised: 22 Dec 2005


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.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Apple Computer, Inc.Affected28 Mar 200501 Apr 2005
Debian LinuxAffected28 Mar 200529 Mar 2005
F5 Networks, Inc.Affected28 Mar 200502 May 2005
Mandriva, Inc.Affected28 Mar 200501 Apr 2005
MiT Kerberos Development TeamAffected-29 Mar 2005
Red Hat, Inc.Affected28 Mar 200522 Dec 2005
Sun Microsystems, Inc.Affected28 Mar 200529 Mar 2005
Microsoft CorporationNot Affected28 Mar 200501 Apr 2005
Cray Inc.Unknown28 Mar 200529 Mar 2005
EMC CorporationUnknown28 Mar 200529 Mar 2005
EngardeUnknown28 Mar 200529 Mar 2005
FreeBSD, Inc.Unknown28 Mar 200529 Mar 2005
FujitsuUnknown28 Mar 200529 Mar 2005
HitachiUnknown28 Mar 200529 Mar 2005
HPUnknown28 Mar 200529 Mar 2005
If you are a vendor and your product is affected, let us know.View More »

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



Thanks to iDEFENSE Labs for reporting this vulnerability.

This document was written by Ken MacInnis.

Other Information

  • CVE IDs: CVE-2005-0469
  • Date Public: 28 Mar 2005
  • Date First Published: 29 Mar 2005
  • Date Last Updated: 22 Dec 2005
  • Severity Metric: 12.60
  • Document Revision: 29


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