How severe is CVE-2026-21243?

CVE-2026-21243 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-21243 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21243?

CVE-2026-21243 primarily affects Microsoft Windows Server 2019. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21243?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-21243 have an EU (EUVD) identifier?

Yes. CVE-2026-21243 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7317.

When was CVE-2026-21243 published?

CVE-2026-21243 was published on 2026-02-10 and last updated on 2026-06-17.

CVE-2026-21243

CVE-2026-21243 is a high-severity vulnerability in Microsoft Windows Server 2019 with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (68th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-7317
Weakness: CWE-476
Affected product: Microsoft Windows Server 2019
Published: 2026-02-10
Last modified: 2026-06-17

Description

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

Frequently asked questions

What is CVE-2026-21243?: Null pointer dereference in Windows LDAP - Lightweight Directory Access Protocol allows an unauthorized attacker to deny service over a network.
How severe is CVE-2026-21243?: CVE-2026-21243 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-21243 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (68th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21243?: CVE-2026-21243 primarily affects Microsoft Windows Server 2019. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21243?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-21243 have an EU (EUVD) identifier?: Yes. CVE-2026-21243 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-7317.
When was CVE-2026-21243 published?: CVE-2026-21243 was published on 2026-02-10 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21243

Affected products (4)

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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