DLL sideloading Archives

Winsage

August 14, 2026

Mustang Panda Adds Signed Windows Rootkit to CoolClient Backdoor for Stealth

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.

Winsage

August 14, 2026

APT group HoneyMyte upgrades CoolClient: the backdoor gets a kernel-level Windows rootkit

CoolClient is a sophisticated backdoor family linked to the HoneyMyte APT group, actively used in cyber-espionage campaigns targeting organizations in Asia and Russia since its initial disclosure in 2022. It has capabilities such as keylogging, clipboard theft, credential harvesting, and system reconnaissance. Investigations in 2023 revealed enhancements, including clipboard theft and HTTP traffic interception. By late 2025 and into 2026, a variant was noted that could deploy a signed kernel-mode driver as a Windows service, improving its stealth and operational capabilities. In a recent campaign targeting Myanmar, the HoneyMyte group used PlugX to deploy CoolClient components. They configured Microsoft Defender to exclude a fake Windows Defender installation directory and a renamed executable, defender.exe, to avoid detection. Persistence was achieved through a scheduled task that executed defender.exe with SYSTEM privileges at startup, which sideloaded the malicious libngs.dll to initiate the CoolClient execution chain. The latest CoolClient variant has a multi-stage execution chain, including: - defender.exe / Sang.exe: Exploited legitimate application for DLL sideloading. - libsrapc.dll: Benign dependency for the Sangfor application. - libngs.dll: First-stage loader that decrypts and loads the next stage. - loadcert.ini: Second-stage DLL implementing core functionalities. - cert.ini: Final-stage implant for command and control communication. - time.ini: Configuration file for CoolClient. The execution begins with the legitimate Sangfor application loading libngs.dll, which uses obfuscation to conceal its operations. The second stage, loadcert.ini, is injected into synchost.exe and performs tasks including persistence and process injection. The kernel-mode driver deployment routine involves decrypting time.ini, verifying privileges, and creating a service to execute the driver, enhancing stealth. The deployed kernel-mode driver, msagent.sys, is digitally signed and helps hide processes, files, and registry objects, making detection more difficult. The latest variant continues to target organizations consistent with previous HoneyMyte activities, with confirmed victims in Myanmar, Mongolia, Pakistan, and Russia, including government entities. The deployment of CoolClient as a secondary backdoor after a PlugX infection indicates a strategic approach to maintain access to compromised systems. The malware is confirmed as a new variant of CoolClient associated with the HoneyMyte threat group, with the kernel-mode driver marking a significant advancement in its capabilities.

Tech Optimizer

July 10, 2026

Hackers Use Fake VLC Executable and Malicious libvlc.dll to Deploy ValleyRAT

Cybercriminals are exploiting the VLC media player to install ValleyRAT, a remote access trojan, by embedding malware in a seemingly harmless file linked in phishing emails. The attack starts with an email that prompts the victim to download a ZIP archive containing a fake VLC executable and a malicious DLL named libvlc.dll. This method uses DLL sideloading to execute the malware under the guise of a legitimate application. Once executed, the malware establishes persistence by creating a registry entry and connects to a remote server to retrieve the final payload. ValleyRAT employs evasion tactics to avoid detection, including assessing system characteristics before executing harmful actions and using a fileless approach to deliver the payload directly into memory. Researchers have identified indicators of compromise, including specific SHA1 hashes and URLs associated with the malicious campaign.