Critical RCE Vulnerability in Microsoft WSUS via Unsafe Cookie Deserialization
Microsoft has released emergency out-of-band security updates to address a critical remote code execution (RCE) vulnerability in Windows Server Update Services (WSUS), tracked as CVE-2025-59287. The flaw, rated CVSS 9.8, allows unauthenticated attackers to exploit unsafe deserialization in the WSUS AuthorizationCookie mechanism, enabling arbitrary code execution with SYSTEM privileges. Proof-of-concept exploit code for this vulnerability is publicly available, increasing the urgency for organizations to patch affected systems immediately. The vulnerability affects only Windows servers with the WSUS Server Role enabled, and Microsoft has provided security updates for all supported Windows Server versions, along with workarounds for those unable to patch immediately.
Security researcher Batuhan Er from HawkTrace detailed that the vulnerability arises from the unsafe deserialization of AuthorizationCookie objects sent to the GetCookie() endpoint, where encrypted cookie data is decrypted and deserialized without proper type validation. This flaw exposes WSUS servers to remote, unauthenticated attacks that require no user interaction and could potentially be wormable between WSUS servers. Microsoft strongly advises administrators to install the provided patches or apply recommended mitigations to prevent exploitation of this critical vulnerability.
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