FishMonger (I-SOON) ports its SprySOCKS backdoor to Windows with a kernel-driver rootkit

ESET disclosed two previously undocumented Windows variants of SprySOCKS, a backdoor it attributes to FishMonger (a.k.a. Earth Lusca / Aquatic Panda / TAG-22), assessed with high confidence as operated by Chinese contractor I-SOON (ESET WeLiveSecurity, 2026-06-16). Previously known only as a Linux backdoor, the Windows builds (WIN_PLUS and WIN_DRV) were deployed in 2023–2024 against foreign-affairs, technology and telecom government bodies in Taiwan, Thailand, Pakistan and Honduras. WIN_PLUS persists as a Windows Print Processor (VSPMsg) and supports 30+ commands over TCP/UDP/WebSocket. WIN_DRV is the notable one: it loads a kernel driver (fsdiskbit.sys, signed with a certificate from the public PastDSE leaked-cert corpus) which memory-loads a second driver to deliver rootkit-class stealth, hiding processes, files, network connections and registry keys, and performing TCP traffic diversion so the backdoor receives operator commands on an arbitrary port that never appears in netstat (BleepingComputer, 2026-06-16). ESET notes limited, unconfirmed telemetry of a possible UEFI bootkit component (potentially CVE-2023-24932-class Secure Boot bypass).

Why it matters to us: Post-deployment detection is hard because the driver actively hides artefacts; the leverage is pre-deployment hygiene. Hunt scheduled-task creation (EID 4698 / Sysmon EID 1) referencing binaries under %SystemRoot%\Fonts\, Image File Execution Options hijacks of vds.exe, and kernel-driver loads (Sysmon EID 6) of drivers signed with PastDSE-derived certificates. Because TCP diversion defeats host network-tab inspection, rely on EDR kernel sensors / ETW for listening-socket enumeration. Validate that vulnerable/revoked drivers are blocked via WDAC/HVCI and the Microsoft vulnerable-driver blocklist.