Microsoft addressed two security bulletins in May's Patch Tuesday release. Security experts said administrators should apply the fixes immediately-because, despite their small size, they address significant threats.
Microsoft fixed a critical vulnerability affecting Windows Server and an important bug in Microsoft Office PowerPoint, according to the Patch Tuesday advisory released May 10. Microsoft also assigned separate "exploitability" scores for newer versions of the software under the "improved" exploitability index ratings.
The team fixed a critical vulnerability (MS11-035) in the WINS component in Windows Server 2003 and 2008. WINS is a name-resolution service that resolves names in the NetBIOS namespace and does not require authentication to use. While usually not available by default in Windows Server, it is commonly used in the enterprise for internal network servers. Administrators who have enabled WINS in Windows Server should apply the patch immediately as attackers could remotely cause a denial of service, according to Wolfgang Kandek, the CTO of Qualys.
"What might make the WINS vulnerability appealing to attackers is that it is a server-side issue," Joshua Talbot, security intelligence manager, Symantec Security Response, told eWEEK.
Unlike other threats, attackers don't have to trick a user into doing anything since it's just a matter of finding a vulnerable server and feeding the machine "a malicious string of data," according to Talbot. It is also a more serious issue on Windows Server 2003 than on 2008 because Windows Server 2008 has built-in protections such as DEP (Data Execution Prevention) and ASLR (Address Space Layout Randomization). However, attackers can still create exploit code to get past those security features, Talbot said.
The other "important" bulletin (MS11-036) addressed a security flaw in all versions of Microsoft Office Power Point except Office 2010. The bug would allow attackers to take full control of the target machine as soon as the user opens a malicious PPT file.
Both WINS and PowerPoint vulnerabilities are fairly significant, according to Tyler Reguly, technical manager of security research and development at nCircle. File-format vulnerabilities are "popular exploits" but WINS is remote code execution, so it was "difficult" to decide which was the "biggest risk today."
Microsoft listed both vulnerabilities using the new exploitability ratings. The PowerPoint bulletin was rated a "1" for a consistent exploit code likely for older software releases, but 0 for latest software because Office 2010 is not affected. The WINS patch was rated a "2" on both the latest and older versions because it affected all versions.
The updated rating system is intended to make it easier for IT administrators to determine their risk level, according to Microsoft.
"With massive updates such as we had in April, it's easy to get overwhelmed. Microsoft's new index simplifies the process, which will help IT administrators to prioritize which patches they tackle first," said Dave Marcus, director of security research and communications at McAfee Labs.
The small release means administrators should "brace themselves for a larger update" in June, according to Kandek.
To complicate things for IT administrators, a fake Patch Tuesday update is making the rounds, according to security researchers at Websense Security Labs ThreatSeeker network. The malware is spread via a link inside an email message supposedly from "Microsoft Canada Co." which informs users that Microsoft has issued a "Security Update for Microsoft Windows OS," wrote Amon Sanniez, associate security researcher at Websense. Clicking on the link downloads the fake patch to the computer and infects the system with a Zeus Trojan variant, according to Sanniez.
It "ties in almost perfectly" with the real Patch Tuesday updates from Microsoft, Sanniez said.
The email looks quite legitimate and shows "some effort" went into the creation, as the message is presented in both English and French, and the display names within the headers actually say the mail originated from Microsoft Canada.
The malicious executable is currently not being detected by most major antivirus products tracked on VirusTotal, so IT managers should be careful that none of their staff members or users click on the link to get the security update. Websense said it is a low-volume threat, possibly aimed at a handful of companies.