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In examining some highlights for this month’s Patch Tuesday releases, IT pros everywhere will have a little less weight on their shoulders because Microsoft shipped a fix for one of the current IE zero-day vulnerabilities being exploited by attackers.

“Without a doubt, the highest priority for most organizations will be to deploy the IE fix which blocks access to the InfoCard control being exploited in targeted watering-hole attacks,” said Craig Young, vulnerability researcher for Tripwire. “As critical as it is, the IE zero-day appears to be a run of the mill ActiveX memory corruption bug.”

“It’s important to note, however, that the fix is not in the traditional IE Cumulative Update (MS13-088) but rather in a separate ActiveX fix (MS13-090),” said Tyler Reguly, technical manager of security research and development at Tripwire.

“Also patched this month is GDI, and while the bulletin wouldn’t normally merit a critical rating, the vulnerability exists in a common API call that may be implemented by numerous third party products. In addition to applying today’s patches, keep an eye out for security updates from other vendors that make use of the built-in WIndows’ graphics libraries,” Reguly added.

One of the more interesting patches this month are for a unique Outlook vulnerability that could allow port-scanning, a Hyper-V vulnerability that could allow Guest OS to Guest OS code execution, and an X.509 issue in schannel.dll that could allow denial of service.

“While these are unique and interesting vulnerabilities, they pose a lot less risk than typical code execution vulnerabilities,” Reguly explained.

There is also MS13-094, which can allow remote attackers to craft S/MIME emails for the purpose of running a port scan from a victim system. This is possible because when viewed in Outlook, the S/MIME message could trigger HTTP requests to arbitrary hosts/ports during signature validation.

“The attacker can then perform a timing analysis to get an idea of which hosts/ports are accessible from the victim machine. This information can be leveraged in future attacks. Microsoft resolved this issue by limiting the number of S/MIME signers processed,” said Young.

Reguly also notes that Microsoft released an update for Direct Access that is not considered a ‘security update.’ The update resolves a known CVE, but Microsoft didn’t deem it worthy of a bulletin.

“Generally this implies the update is a functionality change in the software, rather than a pure security fix. While the process makes sense on paper, it makes it much more difficult for administrators to recognize that additional patches that actually resolve vulnerabilities are available for their systems,” Reguly said. “Regardless of the severity of the issue, not issuing a bulletin decreases security for users of Direct Access everywhere.”

Some of the less critical but more technically interesting bugs include MS13-092. which can allow an administrator using a Hyper-V guest machine to crash the host or gain code execution privileges for another guest. Microsoft has indicated that a reliable denial of service exploit will likely be developed for this vulnerability in the next 30 days.

“For a Hyper-V service provider this would be quite critical as it allows one customer to deny service to other customers sharing the same host system. The fact that guest-to-guest remote code execution is possible makes this vulnerability rather unique and very important for some Hyper-V users,” said Young.

“If a user of one guest OS is able to load malware onto other guests, integrity for the ‘cloud computing’ model goes out the window.”