Windows Remote Access Connection Manager NULL Pointer Dereference DoS

Successful exploitation causes a local denial of service by crashing Windows Remote Access Connection Manager. Because RasMan manages remote access connectivity, exploitation can interrupt VPN and other remote access sessions, degrade administrative workflows, and reduce service reliability on VPN-dependent systems. Repeated triggering can sustain the outage, and some reporting indicates the service may not automatically restart after a crash, extending downtime until manual recovery. There is no evidence in the provided content that this vulnerability provides code execution or privilege escalation.

If patching cannot be completed immediately, reduce exposure by limiting local access to vulnerable systems, enforcing least privilege, restricting interactive logon rights, removing unnecessary local administrator accounts, and disabling or limiting RasMan on systems that do not require remote access functionality. Monitor for repeated RasMan crashes, unexpected service restarts, abnormal VPN negotiation activity, and suspicious activity involving rasman.exe or rascustom.dll in EDR and Windows event logs. Configure service recovery options to automatically restart RasMan on failure, and use application control such as AppLocker or Microsoft Defender Application Control to block unauthorized scripts or binaries that could be used to trigger the flaw locally.

Apply Microsoft's February 2026 security updates for all affected Windows client and server versions. The provided content maps CVE-2026-21525 to cumulative updates across supported Windows releases, including Windows Server 2012/2012 R2/2016/2019/2022/2025 and multiple Windows 10 and Windows 11 versions. Organizations should verify patch deployment through Windows Update, update history, vulnerability scanning, and build validation, and keep systems within Microsoft's support lifecycle.