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Windows CVE-2026-21243

HIGH
NULL Pointer Dereference (CWE-476)
2026-02-10 secure@microsoft.com
Windows Null Pointer Dereference Microsoft LDAP Windows Server 2019 Windows Server 2022 Windows Server 2022 23h2 Windows Server 2025
7.5
CVSS 3.1 · NVD
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Craft malformed LDAP query
  2. Exploit
    Send over network to LDAP service
  3. Execution
    Trigger null pointer dereference
  4. Impact
    Crash LDAP process causing denial of service

Vulnerability Assessment

Weakness
CWE
CWE-476
OWASP Top 10:2025
A10:2025 - Mishandling of Exceptional Conditions
ASVS 5.0
V16 - Security Logging and Error Handling Null pointer safety, defensive checks
MITRE ATT&CK

1 technique across 1 tactic: Impact

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

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Exploitation Conditions

No special conditions — remote unauthenticated exploitation against default Windows LDAP services accepting network connections without authentication requirements.
Impact

CVSS 7.5 (HIGH). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None. Exploitation no authentication required. Exploitable via remote/network.
Exploit ScenarioDerived

A remote attacker without authentication could exploit this vulnerability to compromise the affected system.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Windows LDAP service in Server 2022 and 2022 23H2 is vulnerable to denial of service through a null pointer dereference that can be triggered remotely without authentication. An attacker can exploit this flaw over the network to crash the LDAP service and disrupt directory access functionality. No patch is currently available for this vulnerability.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 22:02 CVSS 7.5

Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network. [CVSS 7.5 HIGH]

RemediationAI

Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.

Affected Packages

microsoft windows_server_2019_10_0_17763_8389 fix: Windows Server 2019 10.0.17763.8389, Windows Server 2019 (Server Core installation) 10.0.17763.8389
microsoft windows_server_2022_10_0_20348_4773 fix: Windows Server 2022 10.0.20348.4773, Windows Server 2022 (Server Core installation) 10.0.20348.4773
microsoft windows_server_2022_23h2_edition_10_0_25398_2149 fix: Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2149
microsoft windows_server_2025_10_0_26100_32370 fix: Windows Server 2025 10.0.26100.32370, Windows Server 2025 (Server Core installation) 10.0.26100.32370

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 4 packages in microsoft

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

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Technical ContextAI · show details

Classified as CWE-476 (NULL Pointer Dereference). Affects Windows Server 2019. Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

NVD PRIMARY 7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

DescriptionCVE.org

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

Executive ViewAI

Why It Matters

A high-severity vulnerability in Windows LDAP services could allow attackers to remotely disable critical directory services, potentially disrupting authentication and access controls across the enterprise. Organizations relying on Active Directory or LDAP-dependent applications face operational continuity risk until remediation is implemented.

Business Impact: High
Compensating Controls

Segment LDAP servers from untrusted networks using firewall rules; implement IP whitelisting for LDAP client connections; deploy network intrusion detection/prevention systems (IDS/IPS) tuned for LDAP null pointer exploitation patterns; disable unnecessary LDAP features or protocols where operationally feasible; monitor LDAP service availability and implement automated alerting for unexpected service terminations; apply Windows security hardening guidelines (DEP/ASLR); consider temporary use of alternate authentication methods where available pending patch release.

Threat Intelligence Overview

EPSS Score
0.1%
Top 82% exploitable
Data Quality
3 sources
Confidence: Low
NVD CVE.org EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
High

Priority Score

38
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +38
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Null Pointer Dereference MEDIUM

A null pointer dereference occurs when a program attempts to access memory through a pointer that has been set to NULL (address 0x0).

Affected Products (CPE)CVE.org

cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*

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Same weakness CWE-476 – NULL Pointer Dereference

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CVE-2016-4957 HIGH
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CVE-2021-3449 MEDIUM
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References

Advisories & patches
ADVISORY https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243

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