If you're still not worried about the latest zero-day attack that's hitting Internet Explorer, maybe you should be. Amid increasingly dire warnings from SANS and other organizations that this could be the next WMF, the Zeroday Emergency Response Team (ZERT) considered it urgent enough to release the first patch for the VML browser bug -- before Microsoft.

ZERT, a nonprofit group made up of prominent security researchers from the vendor and research communities, says it releases these types of patches when zero-day exploits appear to be a serious risk to the public and/or the Internet. That's a time when you just can't wait for the vendor's patch, according to ZERT.

The free patch fixes a flaw in IE that causes a buffer overflow in Microsoft's Vector Graphics Rendering Language (VML) engine that lets an attacker take over a machine. Outlook is also susceptible to this exploit. Microsoft has said it will patch the vulnerability between now and the next Patch Tuesday, October 10.

Randy Abrams, director of technical education for ESET and the former operations manager for Microsoft's Global Infrastructure Alliance for Internet Safety, says Microsoft doesn't -- and can't -- approve third-party patches. It's really a matter of ZERT being able to issue a patch more quickly, he says. Abrams isn't a member of ZERT but works with a group of researchers that belong to ZERT.

"The odds of ZERT causing problems is probably pretty low, but Microsoft has to test against well over a dozen languages, a large number of combinations of Windows versions and applications, and for compatibility with third party apps," he says. "If ZERT's patch breaks, it is a problem. But if the Microsoft patch breaks, then it is magnified exponentially and people start doing stupid things like refusing all patches."

Abrams admits third-party patching is risky business, but then so is going unpatched. "Ultimately, a person should evaluate their risk level and decide upon a third-party patch from a standpoint of knowledge." The rule of thumb should be to use a vendor's patch when it becomes available, he says.

"The patch is a stopgap," Abrams says. "When Microsoft releases its patch, it would be prudent to apply it. Microsoft's patch is supported; ZERT's is not."

So who will grab this patch in the meantime? "Cowboy sys admins," says researcher HD Moore, or "small organizations where a ruinous patch deployment isn't that big of a deal."

— Kelly Jackson Higgins, Senior Editor, Dark Reading