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Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
SecurityTracker Alert ID: 1013575|
SecurityTracker URL: http://securitytracker.com/id/1013575
(Links to External Site)
Updated: Mar 29 2005|
Original Entry Date: Mar 28 2005
Execution of arbitrary code via network, User access via network|
Exploit Included: Yes |
iDEFENSE reported two buffer overflow vulnerabilities in Telnet, affecting several vendor implementations. A remote server can execute arbitrary code on a connected target user's client.|
A remote telnet server can send a large number of specially crafted LINEMODE Set Local Character (SLC) commands to trigger an overflow in the slc_add_reply() function.
Solar Designer has provided the following demonstration exploit:
perl -e 'print "\377", "\372\42\3\377\377\3\3" x 43, "\377\360"' | nc -l 23
A remote server can also return specially crafted characters that will be escaped by the target user's client, overflowing a buffer in the env_opt_add() function.
Arbitrary code can be executed with the privileges of the target user.
Several telnet client implementations are affected.
The vendors were notified on February 18, 2005.
The original advisories are available at:
A remote server can execute arbitrary code on a connected target user's system with the privileges of the target user.|
Several vendors are issuing fixes.|
[Editor's note: Separate alerts will be issued for each vendor fix.]
Linux (Any), UNIX (Any), Windows (Any)|
This archive entry has one or more follow-up message(s) listed below.|
Source Message Contents
Date: Mon, 28 Mar 2005 13:07:09 -0500|
Subject: iDEFENSE Security Advisory 03.28.05: Multiple Telnet Client
Multiple Telnet Client slc_add_reply() Buffer Overflow Vulnerability
iDEFENSE Security Advisory 03.28.05
March 28, 2005
The TELNET protocol allows virtual network terminals to be connected to
over the internet. The initial description of the protocol was given in
RFC854 in May 1983. Since then there have been many extra features added
Remote exploitation of an buffer overflow vulnerability error in
multiple telnet clients may allow execution of arbitrary commands.
The vulnerability specifically exists in the handling of the LINEMODE
suboptions, in that there is no size check made on the output, which is
stored in a fixed length buffer. By sending a specially constructed
reply containing a large number of SLC (Set Local Character) commands,
it is possible to overflow this buffer with server supplied data.
Successful exploitation would allow a remote attacker to execute
arbitrary code in the context of the user which initiated the telnet
process. In order to exploit this vulnerability, an attacker would need
to convince the user to connect to their malicious server. It may be
possible to automatically launch the telnet command from a webpage, for
On opening this page the telnet client may be launched and attempt to
connect to the host 'malicious.server'.
iDEFENSE has confirmed the existence of the vulnerability in the telnet
client included in the Kerberos V5 Release 1.3.6 package and the client
included in the SUNWtnetc package of Solaris 5.9. It is suspected that
most BSD based telnet clients are affected by this vulnerability.
iDEFENSE is currently unaware of any effective workarounds for this
VI. VENDOR RESPONSE
The following vendors have provided official responses related to this
vulnerability. Other vendors may be affected but have not provided an
- ALT Linux
All supported ALT Linux distributions include telnet client derived from
OpenBSD 3.0. The slc_add_reply() buffer overflow vulnerability is
present in all our telnet clients. Updated packages with fixes for
these issues will be released on March 28, 2005.
- Apple Computer, Inc.
Available for: Mac OS X 10.3.8, Mac OS X Server 10.3.8
This is fixed in Security Update 2005-003, which is available at
FreeBSD-SA-05:01.telnet security advisory:
- MIT (Kerberos)
This vulnerability is covered in the following upcoming advisory:
patch against krb5-1.4:
- Openwall Project
The bugs are fixed starting with telnet package version 3.0-owl2.
- Red Hat, Inc.
Red Hat Enterprise Linux ships with telnet and krb5 packages vulnerable
to this issue. New telnet and krb5 packages are now available along
with our advisory at the URLs below and by using the Red Hat Network
Red Hat Enterprise Linux - telnet
Red Hat Enterprise Linux - krb5
- Sun Microsystems Inc.
Sun confirms that the telnet(1) vulnerabilities do affect all
currently supported versions of Solaris:
Solaris 7, 8, 9 and 10
Sun has released a Sun Alert which describes a workaround until patches
are available at:
Sun Alert #57755
The Sun Alert will be updated with the patch information once it becomes
available. Sun patches are available from:
- CyberSafe Limited
The CyberSafe TrustBroker products, version 3.0 or later, are not vulnerable.
- Hewlett-Packard Development Company, L.P.
HP-UX and HP Tru64 UNIX are not vulnerable.
- InterSoft International, Inc.
InterSoft International, Inc. products NetTerm, SecureNetTerm and
SNetTerm are not affected by the slc_add_reply() buffer overflow
VII. CVE INFORMATION
The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0469 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
VIII. DISCLOSURE TIMELINE
02/18/2005 Initial vendor notification
03/28/2005 Coordinated public disclosure
GaŽl Delalleau credited with this discovery.
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X. LEGAL NOTICES
Copyright © 2005 iDEFENSE, Inc.
Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email firstname.lastname@example.org for permission.
Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
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