VRT Advisories

VRT Rules 2005-12-01

Sourcefire VRT Advisory

Date: 2005-12-02


The Sourcefire Vulnerability Research Team (VRT) has learned of a Trojan Horse downloader program that uses a vulnerability in the way that Internet Explorer handles a Javascript event as an attack vector.

The Sourcefire VRT has confirmed that a rule identified as sid 4647, released on November 9, 2005, will generate events when an attempt is made to exploit this vulnerability.


A vulnerability exists in the way Internet Explorer handles the window() function supplied to the javascript "onload" handler as a parameter. The conditions for exploitation occur when a page is opened in the browser that uses <body onload=window();>.

The Delf-DH Trojan downloader uses this vulnerability to exploit vulnerable systems and gives an attacker the ability to download Trojan Horse programs of their choosing onto a vulnerable system.


Sourcefire rule packs released on November 9, 2005 contained sid 4647 that will generate events when an attempt is made to exploit this vulnerability.

Note: Sid 4647 is NOT enabled by default, should customers wish to detect attempts to exploit this vulnerability this rule should be enabled. Instructions on how to do this can be found in the product User Guide.

Additional References:

Microsoft Security Advisory (911302)

Microsoft Malicious Software Encyclopedia

About the VRT:

The Sourcefire VRT is a group of leading edge intrusion detection and prevention experts working to proactively discover, assess and respond to the latest trends in hacking activity, intrusion attempts and vulnerabilities. This team is also supported by the vast resources of the open source Snort community, making it the largest group dedicated to advances in network security industry.