CVE-2021-40456

Name: CVE-2021-40456
Creator: NVD / NIST
Published: 2021-10-13T01:15:09.89+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 2.21%

Last modified Jun 17, 2026

CVE-2021-40456 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Windows AD FS Security Feature Bypass Vulnerability. EPSS estimates a 2.21% chance of exploitation in the next 30 days.

Description

Windows AD FS Security Feature Bypass Vulnerability

Metrics

CVSS 3.1

5.3/10

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

EPSS Probability

2.21%

80.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

Affected Software

Vendor	Product	Versions
Microsoft	Windows Server	20h2
Microsoft	Windows Server 2019	All versions
Microsoft	Windows Server 2022	All versions

References

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40456Patch, Vendor Advisory
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-40456Patch, Vendor Advisory

Timeline

Published: Oct 13, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-40456?

Windows AD FS Security Feature Bypass Vulnerability

How severe is CVE-2021-40456?

CVE-2021-40456 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 2.21% probability of exploitation in the next 30 days.

How do I fix CVE-2021-40456?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-40456?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST