How severe is CVE-2025-53809?

CVE-2025-53809 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2025-53809 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-53809?

CVE-2025-53809 primarily affects Microsoft Windows 11 24h2. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2025-53809?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-53809 have an EU (EUVD) identifier?

Yes. CVE-2025-53809 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-27321.

When was CVE-2025-53809 published?

CVE-2025-53809 was published on 2025-09-09 and last updated on 2026-06-17.

CVE-2025-53809

CVE-2025-53809 is a medium-severity vulnerability in Microsoft Windows 11 24h2 with a CVSS 3.x base score of 6.5. 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-20.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 1% (69th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-27321
Weakness: CWE-20
Affected product: Microsoft Windows 11 24h2
Published: 2025-09-09
Last modified: 2026-06-17

Description

Improper input validation in Windows Local Security Authority Subsystem Service (LSASS) allows an authorized attacker to deny service over a network.

Frequently asked questions

What is CVE-2025-53809?: Improper input validation in Windows Local Security Authority Subsystem Service (LSASS) allows an authorized attacker to deny service over a network.
How severe is CVE-2025-53809?: CVE-2025-53809 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-53809 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-53809?: CVE-2025-53809 primarily affects Microsoft Windows 11 24h2. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-53809?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-53809 have an EU (EUVD) identifier?: Yes. CVE-2025-53809 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-27321.
When was CVE-2025-53809 published?: CVE-2025-53809 was published on 2025-09-09 and last updated on 2026-06-17.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-53809

Affected products (2)

cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*

More vulnerabilities in Microsoft Windows 11 24h2

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CVE-2026-33824 — Critical (CVSS 9.8): Double free in Windows IKE Extension allows an unauthorized attacker to execute code over a network.

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