Spear-phishing for attacks
Blackpoint Cyber said that the hack starts with a spear-phishing message consisting of a link to an encoded archive, which contains a Windows Shortcut (LNK). Running a file prompts a multi-level strain that consists of privilege escalation, compromising Microsoft Defender protections, while downloading extra payloads.
About Matryoshka
Matryoshka is available in two versions: one that supports HTTP-based communication and command execution, and another that uses GitHub for command-and-control (C2), including beaconing, tasking, reconnaissance, file transfer, and secondary payload delivery. HollowFrame is launched via a DLL side-loading pair consisting of the legitimate Python binary ("python.exe") and a rogue DLL ("python311.dll").
"Together, HollowFrame and Matryoshka gave the actor a persistent foothold for remote command execution, Active Directory reconnaissance, file transfer, and deployment of follow-on tooling. These capabilities could support credential theft, lateral movement, and broader domain compromise through additional tools delivered after initial access,” Blackpoint experts Nevan Beal and Sam Decker said.
Attack tactic
The multi-stage hack attacks two endpoints at an unknown law firm. The LNK file mimicked to be Case Documents to lure the victim into opening and triggering a command sequence that deploys PowerShell to get next-stage components from a remote server.
Hollowframe works as a modular loader and persistent framework that assists multiple tactics to deploy auxiliary components, while performing anti-analysis diagnosis to escape running inside sandboxed environments. This is decided based on installed memory, cursor movement, file count in the user profile, and system uptime. Persistence is gained by setting up a scheduled task.
Matryoshka ("version.dll"), a Rust-based backdoor that talks with its C2 server ("45.158.196[.]184:8888") over HTTP to spawn a shell and provide additional tooling, is deployed by unpacking the encrypted container that the Go loader comes with.
Another DLL gained in association with the same activity has been labeled as a version of Matryoshka that uses a private GitHub repository for polling target-specific commands, submitting results, and fetching payloads.
"The repository functioned as a collection of per-host mailboxes, with each victim assigned a dedicated <computer>_<username> directory. These directories contained beacon.json, cmd.json, result.json, and, in some cases, an upload/ tree for file delivery,” Blackpoint said.
