Security Intelligence Operations

Microsoft Internet Explorer versions 5.01 SP4 and prior contain a vulnerability that could allow an unauthenticated, remote attacker to cause an affected application to terminate or execute arbitrary code.

This vulnerability exists due to improper parsing of malformed Cascading Style Sheet (CSS) strings.  An unauthenticated, remote attacker could exploit this vulnerability by convincing a user to visit a malicious website that may corrupt system memory.  This memory corruption could allow the attacker to cause Internet Explorer to close or execute arbitrary code with the privileges of the user who launched the affected application.

Microsoft has confirmed this vulnerability in a security bulletin and released software updates to correct it.

Microsoft Internet Explorer versions 5.01 SP4 and prior are vulnerable when running on Microsoft Windows 2000 SP4 or prior.

Attackers cannot directly exploit this vulnerability, and instead depend on user interaction.  To exploit this vulnerability, an attacker must convince a user to visit a malicious website.  As a result, the attacker could cause the affected application to close or execute arbitrary code with the privileges of the user.  On systems that grant users Administrator privileges, the attacker could execute arbitrary code, resulting in the complete compromise of the affected system.

The update available from Microsoft corrects this vulnerability by adding checks to properly process CSS strings.

Microsoft has released a security bulletin at the following link: MS07-045