IIS Buffer Overflow

Original release date: June 16, 1999
Last revised: June 18, 1999
Source: CERT/CC

A complete revision history is at the end of this file.

Systems Affected

  • Machines running Microsoft Internet Information Server 4.0

I. Description

Buffer overflow vulnerabilities affecting Microsoft Internet Information Server 4.0 have been discovered in several libraries, including libraries that handle .HTR, .STM, and .IDC files.

A tool to exploit at least one of the vulnerabilities has been publicly released.

II. Impact

These vulnerabilities allow remote intruders to execute arbitrary code with the privileges of the IIS server. Additionally, intruders can use this vulnerability to crash vulnerable IIS processes.

III. Solution

Microsoft has released and updated Microsoft Security Bulletin MS99-019, which points to a patch for these vulnerabilities. We encourage you to read this bulletin, available from


We will update this advisory as more information becomes available. Please check the CERT/CC Web site for the most current revision.

Our thanks to Jason Garms and Scott Culp of Microsoft for providing information contained in this advisory.

Copyright 1999 Carnegie Mellon University.

Revision History
June 16, 1999:  Initial release
June 18, 1999:  Added information about .STM and .IDC files.