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CVE-2026-21243

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

No known exploitation. EPSS puts it in the 73rd percentile. Fixed versions are out.

CVSS 3.17.5HighEPSS percentile73rd1.4% chance in 30 daysCISA KEVNot listedNo confirmed exploitation
No public exploit knownFix3 products4 fixed builds listed below

Published Updated Sources: CVE.org, NVD, BDU

NVD CVE.org

What to do

Find your product and version, then upgrade to the build on the right.

  • Microsoft Windows Server 2019Affected: ≥ 10.0.17763.0, < 10.0.17763.8389Upgrade to: 10.0.17763.8389Stated by: CVE record
  • Microsoft Windows Server 2022Affected: ≥ 10.0.20348.0, < 10.0.20348.4773Upgrade to: 10.0.20348.4773Affected: ≥ 10.0.25398.0, < 10.0.25398.2149Upgrade to: 10.0.25398.2149Stated by: CVE record
  • Microsoft Windows Server 2025Affected: ≥ 10.0.26100.0, < 10.0.26100.32370Upgrade to: 10.0.26100.32370Stated by: CVE record

Versions as the sources state them. Full version matrix after sign-in

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

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

In plain language

No plain-language summary for this CVE yet.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS73rd
CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

1.4% chance of exploitation activity in the next 30 days, which ranks it in the 73rd percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

6 events over 135 days, from the signal feeds we watch.

  1. OpenVAS check added
  2. Patch availablerecord updated
  3. Publishedweakness classified, att&ck mapped

Affected products

And 14 more affected products. See all after sign-in

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

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

Scored 7.5 by NVD.

How it is reached

  • Attack Vector NetworkExploitable remotely over the network without any special conditions
  • Attack Complexity LowNo special conditions — the attack can be reliably reproduced
  • Privileges Required NoneNo authentication required — anyone can exploit this
  • User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

  • Scope UnchangedImpact is limited to the vulnerable component itself

Impact if exploited

  • Confidentiality NoneNo confidentiality impact
  • Integrity NoneNo integrity impact
  • Availability HighTotal denial of service — the component is completely unavailable

Weaknesses

ATT&CK techniques

Mapped from the weaknesses above (CWE to ATT&CK), not observed in attacks.

Sources

References in the record

In the news

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