Microsoft has issued a patch for a critical zero-day vulnerability in Windows Remote Desktop Services (RDS), known as CVE-2026-21533. This flaw has been actively exploited by attackers to gain elevated SYSTEM-level access.
Details of the Vulnerability
The vulnerability was addressed on February 10, 2026, as part of Microsoft’s Patch Tuesday updates. The issue arises from improper privilege management within RDS, allowing local attackers to execute privilege escalation without user interaction. With a CVSS v3.1 score of 7.8, the flaw poses significant risks to system confidentiality, integrity, and availability.
Security firm CrowdStrike identified exploit binaries that manipulate service configuration registry keys to facilitate unauthorized access, such as adding new user accounts to the Administrators group.
Impacted Systems and Risks
This vulnerability affects various Windows operating systems, particularly those running RDS. Impacted versions include Windows Server 2025, Windows 11 24H2, Windows Server 2022, and more. The vulnerability is especially concerning for servers where RDS is enabled, serving as a potential vector for lateral movements by threat actors.
Adam Meyers from CrowdStrike has cautioned that attackers in possession of this exploit are likely to increase their efforts in leveraging or distributing it.
Mitigation and Future Outlook
Microsoft strongly advises users to apply the latest security updates and patches immediately. Disabling RDS where not needed, restricting access to trusted networks, and enforcing least privilege principles are recommended mitigation steps. Additionally, deploying endpoint detection and response (EDR) tools can help identify abnormal privilege escalation activities.
The emergence of this zero-day vulnerability underscores the persistent security challenges in older Windows systems. It highlights the need for organizations to prioritize security updates and harden RDS configurations to prevent potential breaches.
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