High7.5Microsoft Server

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

This high-severity Microsoft Server advisory covers CVE-2026-21243 affecting Windows Server 2019 (Server Core installation), Windows Server 2022, 23H2 Edition (Server Core installation), Windows Server 2025 (Server Core installation).

CVE-2026-21243 Published Feb 10, 2026Updated by vendor Aug 19, 2026

CVE-2026-21243

Affected products & platforms

Microsoft ServerWindows Server

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Summary

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

Affected products named by the advisory: Windows Server 2019; Windows Server 2019 (Server Core installation); Windows Server 2022; Windows Server 2022, 23H2 Edition (Server Core installation); and 2 more.

Affected products named by the advisory: Windows Server 2025 (Server Core installation).

Affected versions

Windows Server 2019 10.0.17763.0 before 10.0.17763.8389
Windows Server 2019 (Server Core installation) 10.0.17763.0 before 10.0.17763.8389
Windows Server 2022 10.0.20348.0 before 10.0.20348.4773
Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.0 before 10.0.25398.2149
Windows Server 2025 10.0.26100.0 before 10.0.26100.32370
Windows Server 2025 (Server Core installation) 10.0.26100.0 before 10.0.26100.32370

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

Fixed versions

10.0.17763.8389
10.0.20348.4773
10.0.25398.2149
10.0.26100.32370

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

Mitigation

Upgrade to a fixed release: 10.0.17763.8389, 10.0.20348.4773, 10.0.25398.2149, 10.0.26100.32370. That is the remediation for this advisory.

The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.

Official advisory · high-confidence parse· fetched 2 hours ago·verify at source

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