CVE-2026-21243Network attack vector

Unauthenticated service interruption via LDAP null dereference

Published Feb 10, 2026 · Updated Feb 10, 2026

Null pointer dereference in Windows LDAP on affected Windows Server releases allows remote attackers to interrupt service over a network. Microsoft identifies the locus only as Windows LDAP and has not published the input path or pointer operation that reaches the null dereference. No authentication or user interaction is required, and the documented impact is an availability loss rather than data disclosure or modification.

CVSS severity7.5
High
EPSS probability1.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Null pointer dereference in Windows LDAP on affected Windows Server releases allows remote attackers to interrupt service over a network. Microsoft identifies the locus only as Windows LDAP and has not published the input path or pointer operation that reaches the null dereference. No authentication or user interaction is required, and the documented impact is an availability loss rather than data disclosure or modification.

The record

CVE
CVE-2026-21243
Published
Feb 10, 2026
Updated
Feb 10, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.17763.0 <10.0.17763.8389

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.8389
Microsoft · Windows Server 2025 (Server Core installation)version=10.0.26100.0 <10.0.26100.32370
Microsoft · Windows Server 2022, 23H2 Edition (Server Core installation)version=10.0.25398.0 <10.0.25398.2149
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.8389
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.4773
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.32370

Published CVSS scores

7.5Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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