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Try as they might, ransomware crooks can't hide their tells when playing hands

Sophos sees common behavior across various infections

Common behaviors shared across all families of ransomware are helping security vendors better spot and isolate attacks.

This according to a report from British security shop Sophos, whose breakdown (PDF) of 11 different malware infections, including WannaCry, Ryuk, and GandCrab, found that because ransomware attacks all have the same purpose, to encrypt user files until a payment is made, they have to generally perform many of the same tasks.

"There are behavioral traits that ransomware routinely exhibits that security software can use to decide whether the program is malicious," explained Sophos director of engineering Mark Loman.

"Some traits – such as the successive encryption of documents – are hard for attackers to change, but others may be more malleable. Mixing it up, behaviorally speaking, can help ransomware to confuse some anti-ransomware protection."

Some of that behavior, says Loman, includes things like signing code with stolen or purchased certificates, to allow the ransomware to slip past some security checks. In other cases, ransomware installers will use elevation of privilege exploits (which often get overlooked for patching due to their low risk scores) or optimize code for multi-threaded CPUs in order to encrypt as many files as possible before getting spotted.

"Ransomware creators are acutely aware that network or endpoint security controls pose a fatal threat to any operation, so they've developed a fixation on detection logic," Loman explained.

"Modern ransomware spends an inordinate amount of time attempting to thwart security controls, tilling the field for a future harvest."

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Even with these countermeasures, however, Loman notes that Sophos and other anti-malware vendors have an advantage as they know that, sooner or later, the malware has to access the file system and begin to encrypt the data. This is the point where the attacks have to expose themselves and the spot where security tools can stop them.

"It's important to recognize there's hope in this fight, and a number of ways admins can resist: Windows 10 Controlled Folder Access (CFA) whitelisting is one such way, allowing only trusted applications to edit documents and files in a specified location," says Loman.

"But whitelisting isn't perfect – it requires active maintenance, and gaps or errors in coverage can result in failure when it's most needed."

The report is the latest indication that the good guys are making some headway in the battle against ransomware infections. The Sophos attack comes as other vendors have noted that many state and local governments that had previously been prime targets for ransomware are better protecting themselves, forcing criminals to look to more remote areas in search of low-hanging fruit. ®

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