Vulnerability Note VU#400577

Microsoft Internet Explorer allows arbitrary local file reading via "showHelp()" function

Overview

A vulnerability in Microsoft Internet Explorer (IE) allows remote attackers to read arbitrary files on a vulnerable system.

I. Description

A vulnerability in the showHelp Method contained within IE may allow a remote attacker to read arbitrary files. For further details, please see the following documents:

Although a patch is available, it is important to note that it *disables* the showHelp method, but does not "fix" it. In order to restore the functionality showHelp provides, you must install the latest version of HTML Help. Additionally, the latest version of HTML Help contains some limitations. Quoting from Microsoft Security Bulletin MS03-004:

Only supported protocols can be used with showHelp to open a web page or help (chm) file.
The shortcut function supported by HTML Help will be disabled when the help file is opened with showHelp This change will not affect the shortcut function if the user opens the same CHM file manually by double-clicking on it, or by invoking an application on the local system that uses the HTMLHELP( ) API.

Microsoft recommends using http://windowsupdate.microsoft.com/ to obtain the latest version of HTML Help.

II. Impact

A remote attacker may be able to read arbitrary files on a vulnerable system, which may allow them to gain access to sensitive information such as user credentials. In the worst case, a remote attacker may be able to execute programs with certain parameters leading to a total system compromise if IE is running as administrator.

III. Solution

Apply a patch. More information about patches can be found in MS03-004.

Systems Affected

Vendor	Status	Date Notified	Date Updated
Microsoft Corporation	Vulnerable	6-Feb-2003

References

http://www.microsoft.com/technet/security/bulletin/ms03-004.asp
http://www.microsoft.com/security/security_bulletins/ms03-004.asp
http://online.securityfocus.com/archive/1/310684
http://windowsupdate.microsoft.com

Credit

This vulnerability was discovered by Andreas Sandblad. The CERT/CC thanks Andreas for helping us to understand this vulnerability.

This document was written by Ian A Finlay.

Other Information

Date Public:	2003-02-05
Date First Published:	2003-02-06
Date Last Updated:	2003-02-13
CERT Advisory:
CVE-ID(s):	CAN-2003-1328
NVD-ID(s):	CAN-2003-1328
US-CERT Technical Alerts:
Metric:	28.69
Document Revision:	21

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