The Dyre malware tool, which has emerged as one of the most significant banking Trojans since the takedown of the Gameover Zeus botnet last June, has added an effective new trick for avoiding detection by anti-malware tools.
Security researchers at Seculert recently discovered a new version of Dyre that is able to evade sandbox detection tools by checking how many processor cores the machine has.
If it discovers the machine has just one core it immediately terminates on the system it has infected before it can be spotted, Seculert’s CTO and co-founder Aviv Raff, said in a blog Thursday.
A security sandbox is basically a secure virtualized environment for executing and running unfamiliar or untrusted code to see if it contains any malware. Several security tools are currently available that offer sandboxing as a technique for detecting and blocking malicious code.
Typically, sandboxes are configured with just one processor and one core, to save system resources, Raff said in his blog. So checking the number of cores present on a system, like the latest version of Dyre does, is a simple and effective way for the malware to know if it is running in a sandbox environment or not.
Typically, modern malware tools employ multiple techniques to try and avoid being caught in the sandbox Raff said pointing to a research paper that enumerates some of the methods.
For example, a malware tool might search for a specific process name on the system it has infected to see if it can detect the presence of a sandbox or virtual machine. The goal is to try and find process names like vmsrvc.exe, or vmtoolsd.exe and similar that suggests to the malware that it is running in a virtual environment, the paper noted.
Similarly, some malware tools might look for specific registry entries or publicly known module names used by security sandboxes to detect the presence of one. Others look to see if they can find the backdoor that many virtual machines use to communicate with the guest operating system, the paper noted.
The latest version of Dyre that Seculert observed however relies just on the processor core counting technique to make a determination of whether it is running in a sandbox, Raff said. The reason could be that the malware authors have determined this one particular technique is good enough, he noted.
When Seculert tested several commercial and non-commercial sandbox technologies to see if they could detect the new version of Dyre, not one of them did, Raff said.
It is possible the [the malware authors] conducted their own research and determined that this one particular technique or check was the key to remaining undetected by sandboxing solutions,” he said. He added that Seculert had provided details of its discovery to relevant security vendors.
The new sandbox evasion technique is part of a string of modifications and tweaks that have made Dyre an increasingly potent threat since it first emerged last year. Earlier this year, IBM researchers spotted a new malware campaign where attackers used a Dyre variant dubbed Dyre Wolf to steal more than $1 million from businesses.
In a recent report Dell SecureWorks highlighted Dyre as one of the major new banking Trojans to have emerged in the post-Zeus era.