Vulnerability Note VU#952611

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

Original Release date: 28 Nov 2001 | Last revised: 29 Nov 2001


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


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.


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).


Apply the patch provided by Microsoft at

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 (Learn More)

VendorStatusDate NotifiedDate Updated
MicrosoftAffected-28 Nov 2001
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CVSS Metrics (Learn More)

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



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

  • CVE IDs: CAN-2001-0667
  • Date Public: 10 Oct 2001
  • Date First Published: 28 Nov 2001
  • Date Last Updated: 29 Nov 2001
  • Severity Metric: 30.37
  • Document Revision: 43


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