CVE-2026-21243 Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability
An unauthorized attacker can cause a denial of service in Windows Server LDAP via a null pointer dereference.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-21243?
CVE-2026-21243 is a high-severity vulnerability in Microsoft Windows Server 2019, published on 10 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.
Weakness: CWE-476
Which versions are affected by CVE-2026-21243?
It affects 4 products.
Products include Microsoft Windows Server 2019, Microsoft Windows Server 2022, Microsoft Windows Server 2022 23h2, Microsoft Windows Server 2025.
How do I fix CVE-2026-21243?
No fix has been published for CVE-2026-21243 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-21243 being exploited?
There is no known exploitation of CVE-2026-21243 in the wild and no public exploit code.
Other vulnerabilities in Microsoft Windows Server 2019
- CVE-2026-88102 Microsoft Failover Cluster Remote Code Execution Vulnerability
- CVE-2026-102192 Windows Failover Cluster Denial of Service Vulnerability
- CVE-2026-69577 Microsoft Azure Attestation service and Device Health Attestation Service Information Disclosure Vulnerability
- CVE-2026-96945 Windows Failover Cluster Denial of Service Vulnerability
- CVE-2026-70005 Active Directory Federation Services (AD FS) Security Feature Bypass Vulnerability
Sources
Also known as GHSA-843x-gmwc-22g8.