CVE-2026-21243: CWE-476: NULL Pointer Dereference in Microsoft Windows Server 2019
Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.
AI Analysis
Technical Summary
This vulnerability (CVE-2026-21243) affects Windows Server 2019 (version 10.0.17763.0) and is caused by a null pointer dereference in the Lightweight Directory Access Protocol (LDAP) implementation. Exploitation requires no privileges or user interaction and can be performed remotely over the network. The impact is limited to denial of service, causing the affected system to become unavailable. Microsoft has released an official fix to remediate this vulnerability.
Potential Impact
An attacker can remotely cause a denial of service condition on Windows Server 2019 by exploiting the null pointer dereference in the LDAP service. This results in service unavailability but does not compromise data confidentiality or integrity. There are no known exploits in the wild at this time.
Mitigation Recommendations
An official patch is available from Microsoft to fix this vulnerability. Administrators should apply the update provided in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243 to remediate the issue. No additional mitigation steps are required once the patch is applied.
CVE-2026-21243: CWE-476: NULL Pointer Dereference in Microsoft Windows Server 2019
Description
Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.
CVSS v3.1
Score 7.5high
Affected software
Microsoft
Windows Server 2019
Microsoft
Windows Server 2019 (Server Core installation)
Microsoft
Windows Server 2022
Microsoft
Windows Server 2022, 23H2 Edition (Server Core installation)
Microsoft
Windows Server 2025
Microsoft
Windows Server 2025 (Server Core installation)
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-21243) affects Windows Server 2019 (version 10.0.17763.0) and is caused by a null pointer dereference in the Lightweight Directory Access Protocol (LDAP) implementation. Exploitation requires no privileges or user interaction and can be performed remotely over the network. The impact is limited to denial of service, causing the affected system to become unavailable. Microsoft has released an official fix to remediate this vulnerability.
Potential Impact
An attacker can remotely cause a denial of service condition on Windows Server 2019 by exploiting the null pointer dereference in the LDAP service. This results in service unavailability but does not compromise data confidentiality or integrity. There are no known exploits in the wild at this time.
Mitigation Recommendations
An official patch is available from Microsoft to fix this vulnerability. Administrators should apply the update provided in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243 to remediate the issue. No additional mitigation steps are required once the patch is applied.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- microsoft
- Date Reserved
- 2025-12-11T21:02:05.735Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- official-fix
- Vendor Advisory Urls
- [{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243","vendor":"Microsoft"}]
Threat ID: 698b75ff4b57a58fa1209ff3
Added to database: 02/10/2026, 18:16:31 UTC
Last enriched: 05/12/2026, 05:12:03 UTC
Last updated: 09/10/2026, 22:11:35 UTC
Views: 233
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