Serious XSS flaw haunts Microsoft SharePoint

Microsoft’s security response team has confirmed the existence of a serious cross-site scripting (XSS) vulnerability in the Microsoft SharePoint Server 2007 product.

The vulnerability, which can be exploited via the browser, could allow a malicious hacker to execute arbitrary JavaScript code within the vulnerable application.  A proof-of-concept exploit has been publicly posted and Microsoft is expected to issue a formal security advisory before the end of this week to offer pre-patch workaround and mitigations.

Here’s the skinny on the flaw from an alert posted to the the Full Disclosure mailing list:

The vulnerability exists due to failure in the “/_layouts/help.aspx” script to properly sanitize user-supplied input in “cid0″ variable. Successful exploitation of this vulnerability could result in a compromise of the application, theft of cookie-based authentication credentials, disclosure or modification of sensitive data.

An attacker can use browser to exploit this vulnerability.

On Twitter, Microsoft said it was aware of the issue and promised to issue guidance for affected customers:

This isn’t Microsoft SharePoint’s first brush with XSS security problems.  Back in 2007, the company shipped an “important” security patch to fix a flaw that allowed attackers to run arbitrary script that could result in elevation of privilege within a SharePoint site.