TeslaCrypt Ransomware Group Pulls Plug, Releases Decrypt Key

The somewhat surprising move this week by the operators of the TeslaCrypt ransomware sample, to cease operations and publicly release the universal master decryption key for it, is good news for victims of the malware.

It now means that they have a way to unlock data that might have been encrypted by TeslaCrypt. But the move, welcome as it is, doesn't necessarily mean that the group won’t simply release another sample or start afresh with a new malware campaign altogether, security researchers warned.

Slovakia-based ESET, which has been tracking TeslaCrypt for the past several months, recently noticed an announcement from the group behind the malware of its decision to cease operations. A security researcher at ESET reached out anonymously to the group via its support channel for victims, and asked for the master decryption key. “Surprisingly, they made it public,” the company announced on its blog.

ESET has released a free decryption tool based on the master key that it says can unlock files that were encrypted by any variant of TeslaCrypt. The company has provided instructions on how to use the tool at its ESET Knowledgebase website.

In comments to Dark Reading, ESET security researcher Lysa Myers says it’s unclear what prompted the change of heart within the TeslaCrypt group. “While it’s possible that the authors felt remorse, it’s also possible that they’ve decided to shut down this codebase in favor of starting fresh,” she says.

At the same time though, it does not necessarily mean that the group has suddenly decided to give up writing malware or even that they have abandoned ransomware campaigns, she cautions.

Similar things have happened in the past, she says. As one example, Myers pointed to an incident last year where someone purporting to be the creator of the Locky ransomware sample, apologized for activating the tool and publicly released a decryption key for the malware on PasteBin. Interestingly enough, a year later, Locky continues to be active and is actually the most widely distributed ransomware sample in circulation.

Importantly, releasing the master decryption key does not mean the threat actors behind TeslaCrypt have abandoned malware altogether.

“The most likely scenario is that authors could start fresh with a new codebase, learning from their previous efforts, and then begin infecting people again,” Myers says. “People who were previously infected with the older variant would be an obvious target, as they’ve [shown themselves] to be vulnerable.”

Engin Kirda, co-founder and chief architect
 at cybersecurity firm Lastline says that without direct information from the group behind TeslaCrypt, it is only possible to speculate on their motives.

“In reality, it could be anything,” he says. “It might be that they are moving to a new, illegal online business, or it might be because they are concerned that the authorities have some concrete evidence against them.”

According to Kirda, the mere fact that the master key was publicly released does not mean that TeslaCrypt’s operators cannot resume their operations using new keys and new infectors. “Typically, it is easy to shut down an operation by malware authors, and just as easy to restart it.”

It is also possible that the TeslaCrypt group could start using multiple encryption keys for locking data, so while some data can be released other data might remained encrypted.

“Whatever happens is only limited by the imagination of the malware authors and what they really plan to do,” Kirda says. “We have also seen cases in the past where malware authors have done things just to have fun with security professional such as choosing easily guessable passwords and providing wrong information.”

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