Microsoft Patches 2 Critical Security Vulnerabilities

Microsoft issued fixes for two critical security bugs as part of this month's Patch Tuesday. Arguably the most serious of the flaws impacts Visual Basic for Applications.

Microsoft issued two critical security bulletins today as part of this month's Patch Tuesday.

The release comes a month after the biggest Patch Tuesday of the year, which took aim at 25 bugs. Today's update addresses two bugs; one a vulnerability in Microsoft Visual Basic for Applications, and the other a vulnerability impacting Outlook Express, Windows Mail and Windows Live Mail.

Both vulnerabilities are rated critical and can leave users open to remote code execution by attackers.

"I've put the Visual Basic for Applications (VBA) vulnerability first on my list," said Joshua Talbot, security intelligence manager at Symantec Security Response. "Both vulnerabilities require social engineering to exploit, but the VBA vulnerability requires less action from a user. For instance, an attacker would simply have to convince a user to open a maliciously crafted file-likely an Office document-which supports VBA and the user's machine would be compromised. I can see this being used in targeted attacks, which are on the rise."

Microsoft VBA is used to develop client desktop packaged applications and integrate them with existing data and systems. According to Microsoft, the vulnerability is due to the way VBA searches for ActiveX controls in a VBA-supported document. As a result, it is possible for a host application to pass a specially crafted document with embedded ActiveX controls to the VBA runtime and create a condition where arbitrary could run.

The other vulnerability is caused when a common library used by Outlook Express and Windows Mail insufficiently validates network data before using that data to calculate the necessary size of a buffer.

"An attempt to exploit the vulnerability would not require authentication, allowing an attacker to exploit the vulnerability by sending a specially crafted response to a client initiating a connection to a server under his control using the common mail protocols POP3 and IMAP," Microsoft warned.

Missing from today's patch lineup is a fix for a cross-site scripting flaw affecting Office SharePoint 2007 and Windows SharePoint Services 3.0 first reported April 28. The SharePoint vulnerability permits escalation of privileges within the SharePoint site. If successfully exploited, the bug allows an attacker to run commands against the SharePoint server with the privileges of the compromised user.

Microsoft recommends users concerned about the issue implement the workaround contained in the advisory issued April 29.