Microsoft Patch Tuesday brings critical Explorer, Outlook fixes

Eight of the 13 bulletins issued this month provide fixes for dangerous remote code execution vulnerabilities

Microsoft has shipped fixes for critical vulnerabilities in Internet Explorer and Outlook as part of September's round of vulnerability fixes.

Overall this month, Microsoft issued 13 bulletins -- 4 for them critical -- that cover 47 vulnerabilities found across Internet Explorer, Outlook, SharePoint, Office and the Windows kernel. It is an exceptionally large number of patches for any one month, said Wolfgang Kandek, chief technology officer of IT security firm Qualys.

Of this round of patches, enterprise security professionals should take a look first at MS13-068, which details a vulnerability allowing for remote code execution in Microsoft Outlook, Kandek said.

This remote code execution vulnerability is particularly dangerous because it does not require user interaction to launch.

The flaw lies in how Outlook handles incoming user certificates, which identify the sender of an email. Outlook's certificate parser can recognize only 256 certificates in any one email.

"The programmer [probably] said 'Well, no one would nest more than 256 certificates,' and no one in their right mind would," Kandek said. "But an attacker would. They always go after this sort of thing."

A hacker could nest more than 256 certificates in an email, which would cause a buffer overflow that could place malicious data in the computer's memory. Microsoft failed to add a mechanism that would check to ensure no more than 256 certificates have been submitted to the parser by any single email.

An exploit for this vulnerability would not require the user to click on anything. Code could automatically be triggered simply by displaying the contents of the email message in a preview window.

MS13-069 for Internet Explorer, a collection of 10 patches, should be dealt with as soon as possible as well, Kandek advised. With these vulnerabilities, an attacker could plant malicious code on a Web page that, when visited by an unpatched browser, could take control of the user's machine, said Amol Sarwate, director of Qualys' Vulnerability Labs .

While Microsoft rated bulletins for Microsoft Office Word, MS13-072, and Excel, MS13-073, as important -- rather than critical -- they still could be harmful to the enterprise if not applied, Kandek said.

Both of these bulletins focus on file format vulnerabilities. They require a user to open a file in order to initiate code that would take control of the computer. Kandek pointed out that environments with sensitive data could be subject to spear-fishing attacks that use these vulnerabilities, in which an attacker may devise a way to fool the user into opening a malicious file.

In addition to the Microsoft patches, administrators should also take a look at the critical patches that Adobe also issued Tuesday for Reader and Flash. Users of Google Chrome and Internet Explorer will have the Flash patches applied automatically, Kandek said.

Joab Jackson covers enterprise software and general technology breaking news for The IDG News Service. Follow Joab on Twitter at @Joab_Jackson. Joab's e-mail address is

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