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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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15 events from the most recent confirmed update back to the earliest known activity.
A Metasploit Framework pull request published an exploit module for the unauthenticated WSUS deserialization flaw, further lowering the barrier to weaponization and testing.
Microsoft disclosed that the patch released for CVE-2025-59287 had the side effect of disabling Windows Server hotpatching, creating an operational issue for some customers after applying the fix.
On November 3, reporting said exploitation had affected at least 50 organizations, with Google's Threat Intelligence Group attributing related activity to a newly tracked threat cluster, UNC6512. Eye Security also said two additional threat actors had conducted intrusions against vulnerable WSUS instances.
By early November, defenders reported notable scanning activity against TCP ports 8530 and 8531, likely tied to efforts to find vulnerable WSUS servers for CVE-2025-59287 exploitation.
Reporting on October 30 indicated that some CVE-2025-59287 exploitation activity was being used to deploy the Skuld infostealer, showing post-exploitation monetization beyond reconnaissance.
Security researchers and government advisories warned that thousands of WSUS instances were reachable from the internet, raising concern that compromise of a WSUS server could enable broader internal supply-chain style attacks.
By late October, Google threat researchers were probing exploitation of CVE-2025-59287 as warnings mounted about attacks against exposed WSUS infrastructure.
CISA issued a warning directing U.S. federal civilian agencies to remediate the exploited WSUS vulnerability, advising identification of exposed servers, application of Microsoft's update, and use of mitigations if patching could not be completed immediately.
CISA added CVE-2025-59287 to its Known Exploited Vulnerabilities catalog after reports of in-the-wild exploitation, elevating urgency for remediation across affected organizations.
The Netherlands' NCSC said it learned from a trusted partner that exploitation of the WSUS flaw had been observed on October 24, warning that public exploit availability increased the risk to exposed servers.
On October 24, Eye Security reported scanning and exploitation attempts targeting CVE-2025-59287, including at least one customer compromise using an exploit different from the public proof of concept.
Security firms including Huntress reported attacks beginning on October 23 against internet-exposed WSUS instances, with attackers sending crafted requests, spawning cmd.exe and PowerShell, performing reconnaissance, and exfiltrating results to attacker-controlled infrastructure.
On October 23, Microsoft issued an emergency out-of-band update for CVE-2025-59287, a critical unauthenticated WSUS remote code execution bug affecting Windows Server systems with the WSUS role enabled. Microsoft also recommended rebooting after patching and suggested disabling WSUS or blocking ports 8530/8531 as temporary mitigations.
Researchers published technical details and proof-of-concept exploit code for CVE-2025-59287, describing unsafe deserialization of WSUS AuthorizationCookie objects and making exploitation easier for attackers.
Microsoft initially addressed CVE-2025-59287 in its October 2025 Patch Tuesday updates, but later acknowledged that this first fix did not fully mitigate the WSUS remote code execution flaw.
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Microsoft Windows Server Update Services (WSUS) is affected by **CVE-2025-59287**, a critical unauthenticated remote code execution flaw with a **CVSS 9.8** score that is being actively exploited in the wild. The vulnerability stems from insecure deserialization of `AuthorizationCookie` objects handled by the `GetCookie()` endpoint, allowing a remote attacker to send crafted `POST` requests to WSUS servers exposed on ports `8530` and `8531` and execute arbitrary code as **SYSTEM**. Observed exploitation has involved WSUS-related processes such as `w3wp.exe` and `wsusservice.exe` spawning `cmd.exe` and `powershell.exe`, indicating full server compromise through the update management service. Microsoft has issued an emergency security update for affected WSUS deployments, while defenders have been urged to patch immediately, restart servers after applying fixes, and restrict inbound access to ports `8530` and `8531` or disable WSUS temporarily if patching cannot be completed at once.
Jul 24, 2026
Microsoft released an urgent out-of-band security update to address a critical remote code execution vulnerability in Windows Server Update Services (WSUS), identified as CVE-2025-59287. The flaw was reportedly under active exploitation in the wild, prompting Microsoft to issue a comprehensive fix outside of its regular update cycle. Security advisories and industry news highlighted the severity of the vulnerability and its inclusion in the U.S. CISA Known Exploited Vulnerabilities catalog, underscoring the immediate risk to organizations relying on WSUS for patch management. The vulnerability allowed attackers to potentially execute arbitrary code on affected WSUS servers, posing a significant threat to enterprise environments. Security experts urged organizations to apply the patch without delay to mitigate the risk of compromise. The rapid response from Microsoft and the attention from security agencies reflect the critical nature of the flaw and the ongoing threat landscape targeting core infrastructure components like WSUS.
Jul 12, 2026
A critical remote code execution (RCE) vulnerability was discovered in Microsoft's Update Health Tools (KB4023057), a utility designed to facilitate rapid security updates via Intune. Researchers found that a misconfiguration involving abandoned Azure blob storage allowed attackers to register a storage account and receive requests from vulnerable devices worldwide, enabling arbitrary code execution. Microsoft has since responded to the disclosure, and newer versions of the tool have addressed the issue, but devices running the original version remain at risk if not updated. Separately, a remote code execution vulnerability in Microsoft Windows Server Update Services (WSUS), tracked as CVE-2025-59287, was actively exploited by threat actors to deploy the ShadowPad backdoor malware. Attackers leveraged this flaw to gain system-level access using PowerCat and subsequently installed ShadowPad via `certutil` and `curl`. The exploitation of these vulnerabilities highlights the risks associated with update management tools and the importance of timely patching and secure configuration to prevent compromise by advanced persistent threats.
Jul 12, 2026