filesystem

The threat actor known as HoneyMyte, also referred to as Mustang Panda, has been deploying an upgraded version of the CoolClient backdoor, which includes a signed Windows kernel-mode rootkit. This rootkit enhances the malware's ability to conceal malicious processes, files, registry objects, and command-and-control (C2) network information. Victims have been identified in Myanmar, Mongolia, Pakistan, and Russia, with confirmed targets including government entities. The CoolClient backdoor is deployed as a secondary access layer following an initial PlugX infection. The kernel component activates when CoolClient gains full access to the Service Control Manager (SCM) and the SeTcbPrivilege privilege. If these conditions are not met, the malware bypasses driver deployment and advances to the final-stage implant. Kaspersky has provided indicators of compromise (IoCs), including file hashes, paths, and C2 domains. In a campaign targeting Myanmar, HoneyMyte used PlugX as the initial implant to deploy CoolClient, which involved creating Microsoft Defender exclusions and renaming a legitimate executable for DLL sideloading. Persistence is achieved through a scheduled task that executes the binary with SYSTEM privileges at startup. Execution begins when a legitimate application loads a malicious DLL, which then manages persistence, registry modifications, UAC bypass, process injection, driver deployment, and C2 communications. When privileges are granted, the malware extracts a kernel driver, writes it to disk, and establishes a driver service. The driver is digitally signed with a certificate from Nanjing Ranyi Technology Co., Ltd. The driver receives configuration data from the CoolClient user-mode component and utilizes specific IOCTL requests to register trusted processes and protect filesystem and registry paths. The rootkit can limit access rights to protected processes, hide processes by unlinking them from the active process list, and deny access to protected files and directories. It also filters C2 IPv4 addresses from network information. The driver incorporates 33 IOCTL handlers, but only three were observed in use during standard execution. Kaspersky shared several file hashes related to the malware, including those for the kernel driver and malicious DLLs. This follows earlier disclosures regarding a newer CoolClient variant and a different HoneyMyte kernel-mode rootkit documented in December 2025.