Microsoft is considering plans to release an unscheduled security patch to address a serious security vulnerability in its ubiquitous Internet Explorer web browser.
Malicious hackers are taking advantage of a security bug in the Vector Markup Language (VML) component of IE to infect users visiting specific pornographic, or other maliciously constructed websites.
Opening maliciously constructed emails in Outlook is also a potential risk, especially as attacks targeting the vulnerability are growing in prevalence since their first appearance last week.
Security firms report the increased prevalence of mass mailing lures that attempt to direct surfers to websites hosting VML exploit code, using tricks such as claiming users have received a Yahoo! Greeting Card.
Microsoft, contrary to reports from independent security experts such as the SANS Institute, claims that these attacks remain "limited". But it concedes this situation could change at any time.
In response, Microsoft is pushing hard to develop and test a stable security patch. This patch is nearing sign-off and may be ready for release outside Microsoft's regular Patch Tuesday update cycle, a rare but far from unprecedented move. Microsoft's next Patch Tuesday is due on 10 October, but the IE patch is likely to appear before that, if a posting on Microsoft's Security Response blog is anything to go by.
"We've made some progress in our testing pass for the update and are now evaluating releasing this outside the monthly cycle, as we do any time customers are under threat and we believe we can issue an update that meets our quality bar for widespread deployment. So right now we're looking at where we hit that quality bar and if that occurs prior to the monthly cycle then we will release," writes Microsoft's Scott Deacon. "The primary driver here is quality and protecting customers, not adherence to the monthly schedule."
News of the possibility of an official IE patch from Microsoft comes days after the release of an unofficial patch from a new ad-hoc group of security pros, called the Zeroday Emergency Response Team (ZERT). Microsoft said it welcomes this work, but does not endorse third party updates on general principle. "As a best practice, customers should obtain security updates and guidance from the original software vendor," Deacon writes.
The VML security bug is unrelated to a (still unpatched) flaw in Microsoft's Direct Animation Path (daxctle.ocx) ActiveX control discovered earlier this month. It's unclear when Microsoft will fix this bug and a patch for this may, or may not, come later than that for the VML bug. ®