Old Flaws, New Tricks: CVE-2017-0199 and PowerPoint Abuse

Attackers are using an old vulnerability to distribute malware in a new way. Microsoft PowerPoint files are being used as more effective means of delivering payloads.

CVE-2017-0199, originally a zero-day remote code execution vulnerability, lets attackers run code on target systems using the Object Linking and Embedding (OLE) technology in Windows to deliver malware. It was previously exploited using malicious Rich Text File (RTF) documents, the same technique seen in the DRIDEX banking Trojan.

Attackers who successfully exploited the vulnerability could assume control over target systems and create new accounts with full user rights, install programs, and view, edit, or delete data. Researchers at TrendMicro have found malware exploiting the same flaw but using PowerPoint files for distribution, a technique not previously seen in the wild.

"Attackers are using the PowerPoint Show (PPSX) format -- a slide presentation that starts showing automatically -- in order to reduce the chances that the victim sees anything amiss with the slides," says Mark Nunnikhoven, VP of cloud security at Trend Micro.

PPSX files are designed for PowerPoint viewers, not authors, he continues. While the malicious file is still a full document, the intention is different and most users will automatically execute the presentation. Using PPSX files streamlines payload delivery to a single click.

The initial exploit arrives as a spearphishing email disguised as a message from a cable manufacturing provider. Nunnikhoven explains these attacks have initially targeted electronic manufacturers but this likely has little to do with that specific industry.

"It's not uncommon for new techniques to target specific verticals first," he says. "This speaks more to the attackers' motivations than any particular issue with that vertical."

The emails contain a malicious PPSX attachment, which downloads a file called logo.doc from the C&C server. This runs a PowerShell command to download and execute a file called RATMAN.EXE, a trojanized version of the REMCOS remote access tool (RAT).

Attackers can use the customizable REMCOS RAT to run remote commands and control a system from anywhere in the world. Its capabilities include a download and execute command, keylogger, screen logger, and webcam and microphone recorders.

The trojanized sample discovered by Trend Micro uses an unknown .NET protector, which contains obfuscations that make it difficult to reverse. Since most detection methods for CVE-2017-0199 focuses on RTF, the use of PPSX files allows attackers to evade antivirus detection.

Microsoft issued a patch for CVE-2017-0199 in April that will prevent this method of exploitation. PPSX is simply a more effective means of attacking victims. However, Nunnikhoven acknowledges the reality that systems may have been left unpatched and remain exposed. Legacy systems and business challenges "provide attackers with a lengthy window" to exploit vulnerabilities.

In some cases, there is no patch at all. This vulnerability affects Microsoft Office 2007 SP3, 2010 SP2, 2013 SP1, and 2016. It also affects Windows Vista SP2, Server 2008 SP2, 7 SP1, and 8.1.

"Some of these systems are end of life supporting, which means without an explicit support agreement with Microsoft a patch is unavailable," he continues. "For other systems, the challenges in patching all systems in a timely manner leave organizations at risk."

Legacy systems are "a weak link in the chain," says Nunnikhoven, and attackers can use them to gain footholds into networks where they can find more modern systems to hit. Attackers are continuing to "actively exploit" older systems, he emphasizes, and it's critical for businesses to invest in IT infrastructure.

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