CVE tracker / CVE-2026-21243

CVE-2026-21243

CVE-2026-21243 is the Windows Lightweight Directory Access Protocol (LDAP) Denial of Service Vulnerability. Microsoft rates it Important, CVSS 7.5. It is not in CISA's Known Exploited Vulnerabilities catalog. Published February 10, 2026.

Risk summary

HighDenial of Service
7.5
CVSS v3 base
1.4%
EPSS: chance of exploitation in 30 days
High
Severity
Important
Microsoft's rating
Unlikely
Microsoft: exploitation
No
In CISA KEV

Microsoft describes it: “Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.”

How to fix it

Microsoft lists 7 affected products and the update that fixes each:

What Microsoft changed

Details

Weakness
CWE-476: NULL Pointer Dereference
Publicly disclosed (Microsoft)
No
Exploited (Microsoft)
No
Known exploited (CISA KEV)
Not listed
Published
February 10, 2026
Last revised
February 10, 2026

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References

Microsoft Security Update Guide NVD CVE record CWE

From Microsoft, CISA, NVD and FIRST data; the Microsoft details were read when this page was opened. Check the references above before you act.