Attackers have been exploiting one of the recently-revealed vulnerabilities in Adobe Reader for at least three weeks, security researchers said today, with one estimating the infection count at "many thousands" so far.
On Tuesday, Adobe acknowledged that its popular PDF viewer sported several flaws, and patched them that same day. However, it has yet to spell out the exact number or nature of the bugs.
But one of those vulnerabilities has been actively exploited since at least Jan. 20, said researchers at the SANS Institute's Internet Storm Center (ISC) and VeriSign's iDefense unit. According to Raul Siles, an analyst with ISC, a malicious PDF (Portable Document Format) file has been spreading a Trojan horse from a server based in the Netherlands. The first evidence of the attack, said Siles, came in a Jan. 20 message on an Italian message forum from a user who noted that three of his PCs had been infected, and the attack was traced back to the Dutch IP address.
Siles quoted email he received from iDefense researchers, who said that the malware, a variation of the "Zonebac" Trojan horse, disables a slew of antivirus programs and modifies search results and banner ads.
Although Lau did not cite specific figures, he put the victim tally as "many thousands" and warned users to patch Adobe Reader and Acrobat promptly. "It appears that this PDF-based attack has been quite successful affecting many thousands of users throughout the world," Lau said on the Symantec security blog Saturday.
Lau also speculated that details of the vulnerabilities had leaked before Adobe could patch them. "While it appears that the vulnerabilities were disclosed in a responsible manner, i.e. [the] vendor was informed and allowed to patch before official announcement, the swiftness of the exploit appearing in the wild could suggest that leaks had occurred," Lau maintained.
On Thursday, Adobe added a security advisory to its Web site, but the new alert did not provide any additional details on the vulnerabilities it had patched. In the advisory, Adobe credited iDefense's MacManus, as well as researchers at Google, Fortinet, 3Com's TippingPoint unit and Security-Assessment.com, a New Zealand-based security consultancy, for reporting the bugs.
The new Reader 8.1.2, which can be downloaded from the Adobe Web site or retrieved using the updater bundled with Reader, targets Windows and Mac OS X users. Adobe does not yet have a patched Version 7 of the application, but it said one would be made available at some point.