Vulnerability Note VU#115632

Microsoft Windows help viewer vulnerable to heap overflow

Overview

A vulnerability exists in the Microsoft Windows help viewer application that could allow a remote attacker to execute code of their choosing on a vulnerable system.

I. Description

The Microsoft Windows help viewer (winhlp32.exe) provides application assistance to users through a special type of file (.hlp). The help file format allows for compression of frequently used phrases. When this feature is employed, information about phrases, including size and number, is stored in a table in the help file. An unsafe use of information supplied during decoding of the phrase table could result in an incorrect memory allocation. This error results in a heap memory overflow that can be exploited by a malformed help file that specifies an invalid size in the phrase table.

Note that this vulnerability may only affect versions of Microsoft Windows with certain language packs installed.� The full scope of affected systems is unclear at the current time.

II. Impact

A remote attacker may be able to execute arbitrary code on a vulnerable system through a maliciously crafted help file (.hlp). The malicious file could be introduced to a victim user through a web site or an email message. The intruder-supplied code would be run with the privileges of the user who opened the malicious help file.

III. Solution

The CERT/CC is currently unaware of a practical solution to this problem.

Workarounds

As always, best practices dictate careful handling of all files received from unknown sources. Users should not open help files from unknown or potentially malicious sources.

Systems Affected

Vendor	Status	Date Updated
Microsoft Corporation	Unknown	18-Jan-2005

References

http://www.securityfocus.com/archive/1/385332
http://www.xfocus.net/flashsky/icoExp/index.html
http://secunia.com/advisories/13645/

Credit

Thanks to flashsky fangxing for reporting this vulnerability.

This document was written by Ken MacInnis.

Other Information

Date Public	12/23/2004
Date First Published	06/14/2005 07:46:30 PM
Date Last Updated	06/22/2005
CERT Advisory
CVE Name	CAN-2004-1306
Metric	15.68
Document Revision	14

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