Vulnerability Note VU#810073

Microsoft Windows Secure Channel integer underflow

Overview

A vulnerability in Microsoft Windows Secure Channel security package may lead to execution of arbitrary code.

I. Description

Microsoft Windows Secure Channel (Schannel) security package implements standard network authentication protocols Secure Sockets Layer (SSL) and Transport Layer Security (TLS). A vulnerability exists in the way Schannel handles specially crafted digital signatures from the server during the SSL handshake, which can result in an integer underflow and heap memory corruption. According to Microsoft Security Bulletin ms07-031:

Schannel performs insufficient checks for specially crafted server-sent digital signatures during the SSL handshake.

II. Impact

According to Microsoft Security Bulletin ms07-031 this vulnerability affects different versions of Microsoft Windows differently:

On Windows XP... An attacker who successfully exploited this vulnerability could remotely take complete control of an affected system.

On Windows 2000 this vulnerability could cause the affected system to stop accepting SSL and TLS connections.

On Windows 2003, the vulnerability could cause the affected system to automatically restart.

See Microsoft Security Bulletin ms07-031 for more detailed information.

III. Solution

Update

Microsoft has released an update to address this issue. See Microsoft Security Bulletin ms07-031 for more details.

Do not follow unsolicited links

In order to convince users to visit their sites, attackers often use URL encoding, IP address variations, long URLs, intentional misspellings, and other techniques to create misleading links. Do not click on unsolicited links received in email, instant messages, web forums, or internet relay chat (IRC) channels. Type URLs directly into the browser to avoid these misleading links. While these are generally good security practices, following these behaviors will not prevent exploitation of this vulnerability in all cases, particularly if a trusted site has been compromised or allows cross-site scripting.

Systems Affected

Vendor	Status	Date Updated
Microsoft Corporation	Vulnerable	13-Jun-2007

References

http://www.microsoft.com/technet/security/bulletin/ms07-031.mspx
http://secunia.com/advisories/25620/
http://www.securityfocus.com/archive/1/471203

Credit

This vulnerability was reported in Microsoft Security Bulletin ms07-031. Microsoft credits Thomas Lim of COSEINC with reporting this issue.

This document was written by Chris Taschner.

Other Information

Date Public	06/12/2007
Date First Published	06/14/2007 03:34:43 PM
Date Last Updated	06/14/2007
CERT Advisory
CVE Name	CVE-2007-2218
Metric	24.30
Document Revision	15