ShadowPad Malware Deployed via Exploited WSUS CVE-2025-59287 Vulnerability
Threat actors have exploited a critical deserialization vulnerability in Microsoft Windows Server Update Services (WSUS), identified as CVE-2025-59287, to gain remote code execution with system privileges and deploy the ShadowPad backdoor. The attackers targeted publicly exposed WSUS-enabled Windows Servers, using the PowerCat utility to obtain a system shell and then leveraging legitimate Windows tools such as curl.exe and certutil.exe to download and install ShadowPad from an external server. ShadowPad, a modular backdoor associated with Chinese state-sponsored groups, is loaded via DLL side-loading techniques, specifically using a legitimate binary to execute a malicious DLL payload in memory.
The vulnerability, which was patched by Microsoft in October, allows remote, unauthenticated attackers to trigger unsafe deserialization of AuthorizationCookie objects, leading to full system compromise. Security researchers from AhnLab and others have documented the attack chain, noting that the flaw has been added to CISA's Known Exploited Vulnerabilities catalog and that a public proof-of-concept exploit is available. The incident highlights the ongoing risk posed by unpatched WSUS servers and the sophisticated methods used by threat actors to maintain persistence and evade detection once ShadowPad is installed.
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