BlackMatter ransomware victims reclaim data using secret decryptor

Victims of BlackMatter ransomware have been secretly getting their data back thanks to a flaw in the encryption found by a cyber security company.

According to a blog post, researchers at Emsisoft discovered a critical flaw in the BlackMatter ransomware that allowed them to help victims recover their files without paying a ransom. This action, the firm claimed, prevented millions of dollars from falling into the hands of cyber criminals.

BlackMatter’s predecessor, DarkSide, has been around since August 2020, targeting large private sector organizations that could afford the gang’s demand. BlackMatter took over when the US retaliated, resulting in DarkSide losing control over its own criminal infrastructure. BlackMatter came onto the scene shortly after in July 2021.

Soon after the emergence of BlackMatter, researchers got their hands on BlackMatter’s ransomware code. According to researchers, rumors that BlackMatter could be a repaint of the DarkSide operation were quickly confirmed.

“The very first BlackMatter version turned out to be almost identical to the last DarkSide version, with the only difference being minor incremental improvements. This first version was quickly followed up with multiple new iterations of the BlackMatter payload and, at the time of writing, the latest internal version number of the payload has reached 2.0,” the researchers said.

With the original DarkSide ransomware, researchers had already found a mistake the DarkSide operators had made that allowed them to decrypt the data encrypted by the Windows version of the ransomware without the need for a ransom to be paid, though the gang fixed this flaw on January 12, 2021.

At the time, researchers did not disclose the flaw as the gang would find out. They then told law enforcement and trusted parties about the flaw to enable researchers to decrypt data.

Luckily for researchers, the BlackMatter gang introduced a change to their ransomware payload that allowed them to recover victims’ data once again without the need for a ransom to be paid.

“As soon as we became aware of the gang’s error, we quietly reached out to our partners, who then assisted us in reaching as many victims as possible before they paid BlackMatter’s ransom,” said Emsisoft.

The researchers said that one of the biggest challenges we faced during the operation related to social media, and Twitter in particular. During one of the higher-profile BlackMatter incidents in September 2021, the ransom note was leaked.

“Ransom notes, including BlackMatter’s, contain critical information intended for the victim only, including instructions on how to reach out and communicate with the threat actor. Consequently, anybody who has access to a note can interact with the gang as though they were the victim,” said Fabian Wosar, Emsisoft's CTO.

This meant that the Twitter infosec community got involved and started hijacking negotiations between victims and criminals. This derailed any sort of intelligence gathering by law enforcement and security researchers in the process.

“We have been fighting ransomware for more than ten years, so we understand the frustration the infosec community feels towards ransomware threat actors better than anyone,” said Wosar.

“However, as cathartic as throwing expletives might have felt, it resulted in BlackMatter locking down their platform, and locking us and everyone else out in the process. Unfortunately, that meant one of the most valuable tools we had to reach victims disappeared literally overnight, leading to missed victims who may have unnecessarily paid ransoms.”

Following this, Wosar said that since then BlackMatter has fixed the bug that allowed decryption of the victim’s data.

“However, just because this specific vulnerability has run its course doesn’t mean our work is done. While we are confident that we managed to reach many BlackMatter victims, there are still some victims that we haven’t been able to contact."