GandCrab Developers Behind Destructive REvil Ransomware

The decision by the developers of GandCrab ransomware to "retire" earlier this year after raking in an estimated $2 billion in less than 18 months may have more to do with a shift in focus than a desire to fade away into obscurity.

A new Secureworks analysis of recent ransomware activity has confirmed earlier suspicions that "Gold Garden," the group behind GandCrab, is actively involved in another ransomware variant named REvil that has been wreaking havoc in recent months.

REvil first emerged in mid-April, about a month before Gold Garden announced its retirement from the ransomware scene. Since then the ransomware has been linked to numerous attacks, most notably on nearly two dozen Texas municipalities and hundreds of dentist offices around the country. The malware has been especially notable for its use in so-called "compromise-once-infect-many" attacks on targets with many customers, such as managed service providers (MSPs), Secureworks said.

In the months since GandCrab disappeared, REvil has quickly established itself as one of the most dangerous and prolific ransomware threats in the wild. The group behind it — who Secureworks has dubbed "Gold Southfield" — has been employing the same ransomware-as-a service model that GandCrab employed. Threat actors have used a variety of techniques to distribute REvil, including via an Oracle WebLogic exploit, malicious spam and phishing emails, and through compromised managed service providers.

According to Secureworks, its technical analysis of some early REvil samples uncovered several similarities in code with GandCrab that cannot be explained away by happenstance.

For example, the string decoding function in REvil is nearly identical to the one used in GandCrab. It also uses nearly the same logic and functionality for building command-and-control URLs as GandCrab. There are other artifacts in REvil's code — such as certain debug paths and version numbering patterns — that suggest the first version of REvil might at least have been intended to be the next version of GandCrab, Secureworks said.

Both GandCrab and REvil also have code that prevents the malware from infecting systems based in Russia. While that by itself is not indicative of a link, it does suggest the authors behind both malware strains are from the same region, Secureworks said.

Phony Retirement
Rob Pantazopoulos, a researcher at Secureworks' Counter Threat Unit (CTU), says it's unclear why GandCrab's developers might have suddenly decided to stop further use of that malware.

One reason could be to evade law enforcement. "The threat actors realized that their boisterous nature and researcher-taunting caused some unwanted attention, so they evolved and rebranded under REvil, which, thus far, has been significantly lower key," Pantazopoulos says.

Or it is likely an internal rift occurred among Gold Garden members, resulting in the creation of Gold Southfield with many of the same members from the original group. Regardless of the reasons, since the threat group announced its retirement, GandCrab activity appears to have completely ceased.

Technically, REvil appears to be on par with GandCrab and has more or less the same capabilities. "In my opinion, the significant difference with REvil is the targeting methodologies employed by REvil partners and distributors," Pantazopoulos says.

Since REvil first surfaced, there have been numerous reports of attackers leveraging compromised managed service providers and strategic Web compromises to essentially compromise once and infect many. "For a highly skilled threat actor, this is a low-effort, high-reward scenario," he says.

In a report last month, Fidelis, which has been tracking REvil, described the malware as one of the most active strains during the second quarter of this year. The security vendor estimated REvil as accounting for 12.5% of the ransomware market share compared with about 24% for Ryuk and 17% for the Phobos ransomware strain.

"[REvil] operations have spread wide in the last few months, thanks to different methods, such as malspam, exploit kits, RDP brute-forcing, hacks of MSP, and zero-day exploits," says a spokeswoman from Malwarebytes, another security vendor that has been tracking the malware. The malware has essentially filled the hole created by GandCrab's exit.

"GandCrab was extremely successful, but perhaps its operators decided to refocus their business in ways where they can run operations by focusing on bigger targets," the spokeswoman notes.

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