Gentlemen Ransomware: Evading Detection with EDR Killers
The Gentlemen ransomware-as-a-service (RaaS) is actively developing and maintaining a suite of endpoint detection and response (EDR) killers to help affiliates evade detection in attacks. According to researchers, the gang employs a collection of EDR-killing tools, most notably a utility that has been dubbed GentleKiller.
GentleKiller: A Custom EDR Killer
GentleKiller has at least eight variants and impersonates various legitimate security products, including Kaspersky, Valorant, Javelin, and WatchDog. The tool is used to disable defenses in the early phases of an attack, ensuring that data theft or encryption processes run unencumbered. GentleKiller works by leveraging the 'bring your own vulnerable driver' (BYOVD) technique to elevate privileges and disable security engines.
Each GentleKiller variant uses different vulnerable drivers to achieve kernel-level privileges. However, they all share common strings, identical code obfuscation techniques, and similar process-killing logic and targeting scope. The analysis of the variants indicates that the framework is designed to allow easy driver swaps or weaponization of newly disclosed flaws without requiring major code changes.
Targeting Security Vendors
GentleKiller targets more than 400 processes associated with approximately 48 security vendors/products, such as Microsoft, CrowdStrike, SentinelOne, Palo Alto, Sophos, Trend Micro, ESET, Bitdefender, McAfee/Trellix, and Kaspersky. The binaries for the EDR killer tool are protected by the commercial Enigma and Themida packing and code-protection tools.
ESET notes that the threat actor also uses stolen digital signatures from legitimate software, although they are invalid. Although GentleKiller is a standardized tool used in Gentlemen ransomware attacks, ESET reports that the threat group's collection of EDR killers also incorporates at least three external tools: HexKiller, ThrottleBlood, and HavocKiller.
Additional Tools and Tactics
The researchers' analysis indicates that Gentlemen ransomware picks targets based on the configuration of their FortiGate endpoints. This is particularly interesting given the recent discovery of “FortiBleed,” a collection of nearly 74,000 FortiGate VPN credentials. The Gentlemen RaaS previously compromised the Romanian energy provider Oltenia and has been linked to a SystemBC proxy malware botnet with over 1,570 hosts, believed to be corporate victims.
The Gentlemen RaaS has also been linked to the use of OxideHarvest, a Rust-based credential-stealer tool that the researchers believe, based on the programming language choice, was developed externally. The use of these additional tools and tactics suggests that the Gentlemen RaaS is continually evolving and adapting to evade detection and maximize the effectiveness of their attacks.
Conclusion
The Gentlemen ransomware-as-a-service poses a significant threat to organizations, using a range of tools and tactics to evade detection and compromise systems. The use of EDR killers, such as GentleKiller, and other tools like OxideHarvest, highlights the importance of continually monitoring and updating security systems to stay ahead of emerging threats.
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Source: BleepingComputer