Russian PDF attacks surge; Microsoft takes blame

Evil PDFs are planting Gozi, the Trojan Horse that stole millions in February

Microsoft Corp. yesterday updated a security advisory that addressed a broad flaw in Windows and said it is working around the clock to fix the bug. But it may be too late for many. Security researchers said hackers this morning had amped up attacks using malicious PDF files that exploit the vulnerability.

Helsinki, Finland-based F-Secure Corp. 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 Inc., confirmed that the number of messages hitting mailboxes with rogue PDFs soared today. "PDF exploits are ramping up just in time for the weekend," he said in an e-mail.

The attacks, which began Tuesday, exploit bugs in the Windows versions of Adobe Systems Inc.'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," said Sisk in a posting to a Microsoft company blog. "This change in the threat landscape has triggered our Software Security Incident Response Plan." Microsoft's SSIRP coordinates its investigations with researchers from other vendors. Sisk said Microsoft had developers around the world "working around the clock" to devise a fix.

The reason Microsoft is involved is that while the current attacks are based on malformed 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 updates produced by Adobe and similar fixes issued by Mozilla Corp. for Firefox and Skype for its flagship VoIP software would have been unnecessary if Windows had been patched against problems in URI protocol handlers, which let browsers run other programs via commands in a URL.

This summer, researchers argued over who was responsible for URI protocol handler vulnerabilities that were beginning to surface. Microsoft strenuously denied that its software was at fault until earlier this month, when it issued the advisory Sisk referenced, and said it would create a patch.

"This may be Microsoft's first public acceptance that this bug is in fact a Microsoft vulnerability," said Andrew Storms, director of security operations at nCircle Network Security Inc. Although Microsoft has not set a timeline for rolling out a patch to plug the hole currently used by RBN's PDFs, Storms bet it would be next month. "It's safe to assume Microsoft will attempt to release a patch in time for the November regular patch cycle," he said.

The next scheduled patch day for Microsoft is Nov. 13, more than two weeks away.

The newest PDF-based exploits, said researchers today, are using different subject headings in the spam that delivers the files, and new filenames for the PDF documents. According to F-Secure, the spam messages' subjects now include "Your credit report," "Your Credit File" and "Personal Finance Statement."

Another researcher, Don Jackson of SecureWorks Inc., said yesterday that the malware eventually planted on PCs by the RBN attacks is a new variant of Gozi, a Trojan he pegged in February as responsible for the theft of at least $2 million from bank and credit card accounts.

Gozi then and now works much the same way, Jackson said by telephone yesterday. Any information entered into a Web page form secured by SSL is nabbed, then sent to the RBM hackers. Virtually every log-on for accessing online bank or brokerage accounts and every major e-tailer order form are secured with SSL, and thus in danger of being stolen by Gozi.

Unlike in February, when RBN carelessly exposed a server containing the stolen data -- which Jackson discovered -- the current attack results are unknown. "They've gotten smarter about where they store their data."

If Jackson is right about the RBN hackers' technical skills, the amount they'll steal this time should prod Microsoft to push out a patch sooner rather than later.

"These guys are good," said Jackson. "They're right up there with the Windows kernel developers as far as programming goes. They're very, very talented. And once they have a foot in the door, they can use that [talent] to force their way in."

Copyright © 2007 IDG Communications, Inc.

  
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