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A malware campaign using fake software installers to deliver Winos v4.0, a memory-resident malware, has been tracked throughout 2025. The campaign, dubbed Catena, employs trojanized NSIS installers, reflective DLL loading, and shellcode-embedded INI files to evade detection. It stages payloads entirely in memory, connecting to attacker-controlled servers mainly in Hong Kong. The operation appears focused on Chinese-speaking environments and shows signs of long-term planning by a capable threat group. The infection chain involves multiple stages, including initial NSIS installers, first-stage loaders, and second-stage payloads, ultimately delivering the Winos v4.0 stager. The campaign has evolved over time, adapting its tactics to avoid detection while maintaining core infrastructure and execution logic.

The Winos 4.0 campaign, tracked throughout 2025 and dubbed 'Catena,' represents a sophisticated malware operation leveraging trojanized NSIS (Nullsoft Scriptable Install System) installers to deliver a memory-resident malware payload known as Winos v4.0. The campaign employs advanced evasion techniques including reflective DLL injection and shellcode embedded within INI files (sRDI shellcode), enabling the entire payload to be staged and executed in memory without writing to disk, thereby reducing forensic footprints and detection by traditional antivirus solutions. The infection chain is multi-staged: initial compromise occurs via fake software installers crafted with NSIS, which then deploy a first-stage loader. This loader subsequently executes a second-stage payload that ultimately delivers the Winos v4.0 stager. The malware connects to attacker-controlled command and control (C2) servers primarily located in Hong Kong, indicating a geographically focused infrastructure. The campaign targets Chinese-speaking environments, suggesting a regional or linguistic focus, and is attributed to the Silver Fox APT group, known for long-term, well-resourced operations. The campaign demonstrates adaptability by evolving its tactics over time to avoid detection while maintaining core infrastructure and execution logic. The use of techniques such as reflective DLL injection (T1055.001), execution through trusted binaries (T1218.011, T1218.010), and living-off-the-land binaries (LOLBins) reflects a high level of operational security and sophistication. The malware's memory-resident nature complicates detection and eradication, as it avoids persistent disk artifacts. Overall, the campaign exemplifies a targeted, stealthy approach to malware delivery and execution, leveraging legitimate installer frameworks and advanced code injection methods to maintain persistence and evade defenses.

Detailed information about NSIS Abuse and sRDI Shellcode: Anatomy of the Winos 4.0 Campaign. Get real-time updates, technical details, and mitigation strategies

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