Microsoft said it is working around the clock on a patch for a Windows flaw that is partly responsible for an ongoing attack wave of infected PDFs.
The company has updated a security advisory to reflect the fact that exploit code is in the wild, but it may be too late for many. Security researchers said hackers have ramped up attacks using malicious PDF files that target the vulnerability.
F-Secure called the surge in spam carrying the rigged PDF documents "massive" and said the run is ongoing. Ken Dunham, director of response at iSight Partners, confirmed that the number of rogue PDFs soared on Friday.
The attacks, which began last Tuesday, exploit bugs in the Windows versions of Adobe's Reader and Acrobat software. Adobe patched the newest editions of those programs Monday, but has not yet updated older variants.
According to Dunham and other researchers, the infamous Russian Business Network (RBN), a collective of cybercriminals, is behind the PDF assault. When recipients open an attack PDF, a combination of Trojan Horses, downloaders and rootkits strike, knocking out the Windows firewall and installing code that captures all information entered into any SSL-secured form on a web page. That information is then transmitted back to RBN.
Microsoft updated its security advisory because it detected what it called "fairly limited" attacks using PDFs, said Bill Sisk, a member of the Microsoft security response team.
"This week we became aware of publicly disclosed exploit code being used in limited attacks on customers," Sisk wrote on a Microsoft blog. "This change in the threat landscape has triggered our Software Security Incident Response Plan." Microsoft's SSIRP coordinates investigations with other vendors. Sisk said Microsoft had developers around the world "working around the clock" on a fix.
While the attacks use PDFs, the real vulnerability lies in Windows XP and Windows Server 2003 code, not in Adobe's, Sisk acknowledged. "The vulnerability mentioned in this advisory is in the Microsoft Windows ShellExecute function," he said. "These third-party updates [such as Adobe's fix] do not resolve the vulnerability, they just close an attack vector."
His admission is the clearest yet from Microsoft that the a patch for problems in Windows URI protocol handlers would have made recent patches in Acrobat, Firefox and Skype unnecessary.