CVE-2026-21243: Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability

High severity · published Feb 10, 2026

CVE-2026-21243

Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability

7.5

CVSS

1.4%

EPSS

On KEV

Description

Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)1.4% · higher than 73% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

Windows Server 2019 · Microsoft

10.0.17763.0 before 10.0.17763.8389 · source: vendor, NVD

Windows Server 2019 (Server Core installation) · Microsoft

10.0.17763.0 before 10.0.17763.8389 · source: vendor

Windows Server 2022 · Microsoft

10.0.20348.0 before 10.0.20348.4773 · source: vendor, NVD

Windows Server 2022, 23H2 Edition (Server Core installation) · Microsoft

10.0.25398.0 before 10.0.25398.2149 · source: vendor

Windows Server 2025 · Microsoft

10.0.26100.0 before 10.0.26100.32370 · source: vendor, NVD

Windows Server 2025 (Server Core installation) · Microsoft

10.0.26100.0 before 10.0.26100.32370 · source: vendor

Windows Server 2022 23h2 · Microsoft

before 10.0.25398.2149 · source: NVD

Affected product

Windows Server 2019

Microsoft

All Windows Server 2019 CVEs

References

NVD

https://nvd.nist.gov/vuln/detail/CVE-2026-21243

CVE.org

https://www.cve.org/CVERecord?id=CVE-2026-21243

Vendor Advisory

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243