Microsoft released 17 security bulletins, including nine that are rated "Critical" and eight rated "Important" as part of its April Patch Tuesday update on April 12. Fifteen of the bulletins address vulnerabilities that allow attackers to remotely execute code.
Not only is this the biggest Patch Tuesday for 2011, it is the largest to date from Microsoft. Patch Tuesday on December 2010 also had 17 bulletins, but addressed 40 bugs. The October 2010 update fixed 49 bugs.
Microsoft addressed 30 "elevation of privileges" vulnerabilities within the Windows kernel in a single bulletin (MS11-034), which is one of the reasons behind the massive update this month, according to Jason Miller, data team manager at Shavlik Technologies. These vulnerabilities in the heart of the Windows operating system could be used by attackers to circumvent processes such as user access control and immediately give a program full administrative privileges on the compromised system.
At least some of the kernel updates for Windows Vista and Windows 7 should have been pushed as security updates instead of waiting for Patch Tuesday, Roel Schouwenberg, a Kaspersky Lab expert.
"As attacks have become more sophisticated it's become more obvious integrity is crucial. To not see Microsoft recognize this is rather surprising," Shouwenberg said.
There have been more escalation of privilege bugs than remote code execution ones in Microsoft's newer products, said Shouwenberg. The trend is likely to persist.
Microsoft recommended administrators first patch Internet Explorer, and then apply the two Server Message Block patches before updating the remainder of the update.
The Internet Explorer patch (MS11-018) affects IE 6, 7 and 8 and drive-by download issues. Users with unpatched browsers visiting a malicious Website are compromised automatically, without having to do anything in this kind of an attack. The object management memory corruption issue in IE 8 that was exploited at the CanSecWest Pwn2Own hacking competition in March is covered under this bulletin.
There were two fixes for the Server Message Block protocol in Windows. The server bug allows attackers to send a specially crafted packet to servers running SMB to take over the machine (MS11-020). The second bug is on the client side and allows attackers to take over the workstation when a user clicks on a link to an external SMB server in an email attachment (MS11-019). For organizations that don't make SMB accessible over the Internet, the main risk comes from inside the network, as attackers who have already broken into the network will be able to exploit the unpatched hole to jump around different servers, Wolfgang Kandek, CTO of Qualys, wrote on The Laws of Vulnerabilities blog.
It's similar to the vulnerability the Conficker worm exploited last year, according to Andrew Storms, director of security operations at nCircle.
Microsoft said the Office File Validation tool is now available for Office 2003 and 2007. Originally announced in December, the feature is native to Office 2010 and determines if an Office document is adhering to the file format specification. Simply put, it will not allow malformed documents to be opened, protecting users from malicious email attachments.
While a "good development," it won't stop the recent Flash zero-day exploits embedding malicious Flash code in Excel spreadsheets or the latest exploit using Word documents, as executive Flash is a "feature and not a bug," according to Schouwenberg. "Hopefully Microsoft will be able to back-port the Office 2010 sandbox at a later date as the sandbox is able to stop the Adobe Flash zero-days," Schouwenberg said.
Microsoft also patched the MHTML flaw (MS11-026) that would allow attackers to run scripts in the wrong security context on Windows XP, Vista, Windows 7 and all supported Windows Server releases. An attacker could exploit the vulnerability to inject a client-side script in a Website the user is viewing in Internet Explorer. First reported in January, Google warned users of actual attacks exploiting the vulnerability on March 11.
"Sixty four vulnerabilities is a very large amount, so organizations should be prepared," said Dave Marcus, McAfee Labs director of security research and communication.