international collaboration

Bitdefender researchers have identified advanced techniques used by the Curly COMrades threat actor, believed to have Russian backing, to exploit Microsoft’s Hyper-V virtualization platform. This group activates Hyper-V on compromised systems to deploy a lightweight virtual machine (VM) running Alpine Linux, which hosts malware tools CurlyShell and CurlCat. The operation began in early July with commands that activated Hyper-V and prepared the environment for the VM, using deceptive file names to avoid detection. The Alpine Linux VM is customized for each victim, allowing the attackers to maintain a low profile while facilitating reverse shell and proxy activities. The VM routes traffic through the host's network, masking communications as originating from the legitimate host IP. CurlyShell acts as a persistent reverse shell, while CurlCat manages SSH traffic tunneling, utilizing a private key for authentication. The attackers also employ various proxy and tunneling tools and utilize PowerShell scripts for tasks such as injecting Kerberos tickets into LSASS for lateral movement and creating local accounts to ensure ongoing access. Their command and control infrastructure involves compromised servers that relay traffic between infected hosts and the attackers' servers, with measures taken to limit forensic evidence. To detect and mitigate these threats, Bitdefender emphasizes the need for host-based network inspection and hardening, as well as monitoring for abnormal access to the LSASS process and suspicious Kerberos ticket activities. The findings indicate a shift in threat actor tactics towards using virtualization for stealth and persistence, highlighting the need for layered security measures.