Escalating attacks exploiting a serious weakness in PDF files have prompted Microsoft to issue an all-hands-on-deck call to fix a vulnerability that lurks in the bowels of Windows XP.
"We currently have teams worldwide who are working around the clock to develop an update of appropriate quality for broad distribution," Bill Sisk, a member of Microsoft's security response team wrote in a blog post Thursday. "Because ShellExecute is a core part of Windows, our development and testing teams are taking extra care to minimize application compatibility issues."
In the meantime, users should take extra care when receiving email attachments, even when delivered from known sources, and when visiting familiar or unknown websites, Sisk said. He didn't mention updates Adobe has issued here for its Reader program or here, but installing them immediately is also critical.
Sisk's warning is being prompted by a flurry of spam-carrying rigged PDF files that exploit the vulnerability. Based on reports by independent researchers, the emails appear to be on the rise. According to Ken Dunham, director of global response for iSIGHT Partners, one source of his intercepted more than 75,000 hostile PDF attachments in the past few days, a rate that translates to one sample every 10 seconds.
"Multiple private sources are now reporting a high volume of emails containing hostile PDF attachments," Dunham wrote in an email.
F-Secure is also reporting malware-tainted PDF are "being spammed heavily through email."
The urgency and transparency Microsoft is showing is commendable. But let's not forget that for more than three months, Redmond's security pros maintained that weaknesses resulting when third-party applications passed malicious uniform resource identifiers (URIs) to Internet Explorer was "not a vulnerability in a Microsoft product." As such, Redmond maintained, responsibility for plugging the hole lay elsewhere.
Two weeks ago, the software juggernaut, (which, incidentally, stunned Wall Street yesterday with strong quarterly earnings, largely on the sale of desktop titles) reversed itself on this position, admitting for the first time that the URI-handling weakness was an issue that had to be addressed by Microsoft.
The change of heart came as it became increasingly clear that the URI-handling weakness was doomed to repeat itself over and over on countless third-party apps. As Sisk put it, "...these third party updates do not resolve the vulnerability - they just close an attack vector."
Microsoft isn't due to issue another patch batch until November 13. ®