Google's VirusTotal puts Linux malware under the spotlight

As Linux malware matures, Google's malware checker will give samples the same treatment as those uploaded for Windows.
Written by Liam Tung, Contributing Writer

The rise of malware designed to infect Linux servers has earned it greater attention from VirusTotal, the Google-owned go-to tool for malware hunters.

For security researchers that need to stay on top of emerging malware threats, the VirusTotal malware database has become an integral tool.

Anyone can upload a suspicious file to the web tool to check whether the dozen or so antivirus engines, such as Kaspersky, McAfee, Symantec, and others, detect it as malware. The tool is meant to be used by the good guys, but as one researcher found last year, black hat hackers were also using the service to test their malware against antivirus products prior to releasing it in the wild — despite the tool's shortcomings for comparative analysis.

While VirusTotal maintains detailed information about malicious files affecting Windows, Linux malware has remained something of a blind spot for the tool, in part because such malware is much rarer. The tool offered basic information about each Linux file sample, but lacked additional information that AV companies and researchers were given for Windows malware.

That situation might have been fine in the past. However, over the past two years, a new breed of Linux malware has emerged whose chief targets are not PCs but vulnerable web servers.

One of the best-known attacks was dubbed Mayhem, a Russian/Ukrainian threat which targeted *nix servers — shorthand for Unix and Linux. Before that, researchers discovered hackers using Linux Cdorked malware, which also aimed for web servers as a platform to distribute Windows malware.

In part due to the lack of information, antivirus vendors were slow to respond to Linux malware samples, often submitted as ELF files — the standard binary file format for executables, object code, shared libraries, and core dumps for Unix and Unix-like systems. As such, detection rates by AV vendors remained low. Now the number of ELF files submitted is rising: in the last week alone, there were over 35,000 suspicious ELF files submitted to VirusTotal, slightly less than the 44,000 suspicious Microsoft Word files uploaded.

VirusTotal announced on Tuesday that it will be addressing the shortcomings with the web tool for Linux malware. "Even though the popularity of the Windows OS among average end-user systems has meant that attackers have mostly focused on developing malware for Windows systems, ELF badness is a growing concern," the Google subsidiary wrote in a post on Tuesday.

It will now provide the same level of detail for ELF files as it does for for Windows-based malware, such as .EXE files and DLL files.

Credit for the new ELF descriptions has been given to security researchers at the organisation Malware Must Die, which has discovered most of the ELF malware over the past two years. The group of researchers were the first to spot and detail Linux malware that exploited the recent shellshock bug in Bash and were the first to spot Mayhem.

A spokesman for Malware Must Die told ZDNet the additional detail about malicious ELF files may help boost detection rates among AV vendors. "The Ukraine/Russia-based Mayhem, and the cDorked ELF malware were all having very low detection rates among antivirus engines," he said, adding that only around four antivirus products recognised them.

After it raised awareness of ELF, the detection rate raised to about 15 to 20 antivirus engines.

More recently, there's been an uptick in the use of ELF malware among suspected Chinese hackers that target web servers to launch distributed denial-of-service attacks, as well as compromise insecure routers and embedded systems. 

He added that additional information VirusTotal provides about ELF samples will help researchers who don't understand UNIX to "mass identify" new samples and ultimately drive better detection rates among AV products. 

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