Vulnerability Note VU#952611

Microsoft Internet Explorer (IE) calls telnet.exe with unsafe command-line arguments ("Telnet Invocation")

Overview

A telnet client can be invoked with unsafe options by arbitrary HTML ("web") pages when rendered by affected Microsoft Internet Explorer clients.

I. Description

This vulnerability is also known as the "telnet logging" or "telnet invocation" or "Microsoft IE Telnet Client File Overwrite" vulnerability. A similar vulnerability was first described in Microsoft Security Bulletin MS01-015.

When vulnerable versions of Internet Explorer render HTML with malicious 'telnet:' tags, the telnet.exe client can be called with unsafe arguments. A telnet option may be specified which directs transcripts or logs of a telnet session to overwrite or create arbitrary files on a victim's system. These files could contain data chosen by an attacker to gain further privileges on a target system.

The telnet package used may be installed as part of the Services for UNIX 2.0 package on computers that are running Windows NT 4.0, Windows 2000, or Windows XP.

II. Impact

A remote attacker may write files onto the system of a user who either visited a malicious web site or opened malicious HTML-formatted mail.The vulnerability could be used to place a file onto the victim's computer which could then run automatically each time the user logged on (i.e., a file installed in the victim's Start folder can allow arbitrary commands to be executed).

III. Solution

Apply the patch provided by Microsoft at

http://www.microsoft.com/windows/ie/downloads/critical/q306121/default.asp

Note this patch can only be applied after having upgraded to Internet Explorer 5.5 Service Pack 2 (SP2), Internet Explorer 5.01 SP2, or having applied the patch fixing the original vulnerability, Q28043.

No previous updates are needed to patch and remove this vulnerability in Internet Explorer 6 clients.
Alternately, remove the telnet client installed as part of the "Services for Unix 2.0" package, if installed.

Systems Affected

Vendor	Status	Date Notified	Date Updated
Microsoft	Vulnerable	28-Nov-2001

References

CERT Advisory CA-2001-21 discusses separate issues involving buffer overflows in implementations of the telnet daemon.
http://www.microsoft.com/technet/security/bulletin/MS01-015.asp
http://www.microsoft.com/technet/security/bulletin/MS01-051.asp
http://www.microsoft.com/windows/ie/downloads/critical/q306121/default.asp
http://www.microsoft.com/windows/ie/download/critical/q286043/default.asp
http://support.microsoft.com/support/kb/articles/Q286/0/43.ASP
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2001-0150
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2001-0667
http://www.securityfocus.com/bid/2463
http://www.cert.org/advisories/CA-2001-21.html
http://www.ciac.org/ciac/bulletins/l-061.shtml
http://xforce.iss.net/static/6230.php

Credit

This variant of the IE "Telnet Invocation" vulnerability first discussed in CVE-2001-0150 was discussed in Microsoft Security Bulletin MS01-051.

This document was written by Jeffrey S. Havrilla.

Other Information

Date Public:	2001-10-10
Date First Published:	2001-11-28
Date Last Updated:	2001-11-29
CERT Advisory:
CVE-ID(s):	CAN-2001-0667
NVD-ID(s):	CAN-2001-0667
US-CERT Technical Alerts:
Metric:	30.37
Document Revision:	43

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