New Malware Variant Targets Old Adobe, Office Vulnerabilities

Organizations that do not patch critical vulnerabilities in the software they use can remain exposed to attacks indefinitely.

A case in point is a new malware variant that researchers at Trend Micro discovered targeting vulnerabilities that were discovered more than six years ago in Adobe Acrobat, Adobe Reader, and Microsoft Office software. Both companies had issued patches.

The malware is a variant of the Asruex Backdoor associated with DarkHotel, a group known for targeting business hotel visitors via hotel Wi-Fi networks. Asruex has been around since at least 2015 and allows attackers to take complete remote control of infected systems. It infects systems via a shortcut file, which, when opened, executes a PowerShell command that ultimately results in Asruex being downloaded on the system. The malware is designed to spread through network drives and removable drives, Trend Micro explained in an advisory this week.

The variant using the patched vulnerabilities itself, however, only surfaced about a year ago. It seems explicitly designed to target organizations using unpatched versions of Adobe Reader 9.x up to before 9.4 and Acrobat versions 8.x up to before 8.2.5 on Windows and Mac OS X, Trend Micro says. "Because of this unique infection capability, security researchers might not consider checking files for an Asruex infection and continue to watch out for its backdoor abilities exclusively," Trend Micro warned.

The impacted versions of both the Adobe and Microsoft software are no longer supported.

Trend Micro researchers found the variant in a PDF file that had been infected with Asruex.  Their analysis showed the variant is designed to exploit two old vulnerabilities: a 2012 critical buffer-overflow issue in an ActiveX component in MS Office versions 2003, 2007, and 2010 that enabled remote code execution (CVE-2012-0158); and a 2010 stack-based buffer overflow in the Adobe products that could be used to inject code into PDFs (CVE-2010-2883). The Adobe flaw was a zero-day and was already being actively exploited in the wild when it was first disclosed.

In the advisory, Trend Micro described the Asruex variant as using infected PDF files and Word documents to drop and execute the malware on systems running unpatched versions of the vulnerable software. 

When the infector is executed on vulnerable versions of Adobe Reader and Adobe Acrobat, it displays the content of the original PDF file while silently dropping the malware in the background. The malware contains several anti-bugging and anti-emulation features and can detect if it is running in a sandbox environment, Trend Micro says.

According to the security vendor, the Asruex variant it discovered uses a special template to exploit the Office vulnerability to infect Word documents. As with PDF files, the variant allows attackers to execute arbitrary files on a system, but with a Word document. When the Word infector is executed, it runs in the background while displaying the original content of the Word document to trick users into believing everything is normal, Trend Micro said.

The Asruex variant poses a challenge for organizations still using versions of the software the malware is targeting, Trend Micro said. "Understandably, this could pose a challenge for organizations as updating widely used software could result in downtime of critical servers, and it could be costly and time consuming," the security vendor said. 

Such malware highlight the need for organizations to follow best practices when it comes to patching and updating critical software, it added.

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