Winsage
September 15, 2026
A spear-phishing campaign linked to the Chinese threat actor UTA0560 targeted various NGOs on September 1, 2026, exploiting recently patched vulnerabilities in Google Chrome and Microsoft Windows. The campaign utilized a malicious JavaScript backdoor called GRIMWEDGE, which was deployed through a multi-stage exploit chain that involved three vulnerabilities: CVE-2026-85046, CVE-2026-87491, and CVE-2026-85880. The attack began with spear-phishing emails that led recipients to a vulnerable U.S.-based university website, allowing attackers to redirect users to their infrastructure.
The exploit chain enabled arbitrary code execution and facilitated the deployment of GRIMWEDGE, which is capable of host reconnaissance, file and process management, command execution, and payload delivery. The initial payload was an executable named "msgbox.exe," which extracted a legitimate Windows binary and a malicious DLL called "wsc.dll." This DLL initiated a sideloading chain and contacted a command-and-control server for further instructions.
GRIMWEDGE allows for several commands, including system reconnaissance, directory listing, file deletion, and command execution in a hidden window. It lacks built-in persistence or lateral movement mechanisms but provides a foothold for further exploitation. Concurrently, another Chinese threat actor, JungleBamboo (APT31), used the same exploit chain to deploy a loader named SUPERSTOMP, which installs a credential-stealing Chrome extension called LONGTALE. The simultaneous use of the exploit chain by multiple actors suggests potential sharing or sale of the exploit, raising concerns about patch-gap vulnerabilities that pose risks for exploitation campaigns.
