The Cybersecurity and Infrastructure Security Agency (CISA) has issued an urgent warning about active exploitation of a critical vulnerability affecting Windows Server Update Service (WSUS).
The agency updated its alert on October 29, 2025, adding crucial information about identifying vulnerable systems and detecting potential threats.
Critical Flaw in Windows Server Update Service
Microsoft released an emergency security update to address CVE-2025-59287, a remote code execution vulnerability impacting WSUS across multiple Windows Server versions including 2012, 2016, 2019, 2022, and 2025.
This vulnerability emerged after a previous patch failed to fully resolve the security issue, leaving systems exposed to attacks.
The severity of this flaw cannot be overstated. Unauthenticated attackers can exploit this vulnerability to achieve remote code execution with system-level privileges, giving them complete control over affected servers.
CISA added CVE-2025-59287 to its Known Exploited Vulnerabilities Catalog on October 24, 2025, confirming active exploitation in the wild.
CISA strongly urges organizations to take immediate action. The first step involves identifying vulnerable servers by checking if WSUS Server Role is enabled and whether ports TCP 8530 or TCP 8531 are open.
Administrators can verify WSUS installation by running a PowerShell command or checking the Server Manager Dashboard.
Organizations must apply the out-of-band security update released on October 23, 2025, to all identified servers.
A system reboot is required after installation to complete mitigation. For organizations unable to deploy the update immediately, CISA recommends temporarily disabling the WSUS Server Role or blocking inbound traffic to the default WSUS listener ports.
After securing WSUS servers, organizations should apply updates to all remaining Windows servers and reboot them to ensure complete protection. Beyond patching, CISA recommends monitoring for signs of exploitation.
Security teams should investigate suspicious activity and child processes spawned with system-level permissions, particularly those originating from wsusservice.exe or w3wp.exe processes. However, these processes may also represent legitimate system activity.
Organizations should monitor for nested PowerShell processes using base64-encoded commands, which attackers commonly use for obfuscation.
Endpoint security platforms should be configured to alert on unusual process behavior and privilege escalation attempts.
CISA updated its guidance to include resources from Huntress and Palo Alto Networks Unit 42.
These organizations have published detailed technical analysis and detection guidance for CVE-2025-59287.
The vulnerability poses a significant risk to organizations running Windows Server infrastructure.
With active exploitation confirmed, delayed patching could result in complete system compromise and potential lateral movement across networks. Security teams should prioritize this update in their patch management schedules.
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