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Fencer Intel
high 7.5

CVE-2021-40456 json

Windows AD FS Security Feature Bypass Vulnerability

published 5y ago modified 4mo ago also EUVD-2021-27633

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.3%
EPSS 2.3% chance of exploitation in 30 days, percentile 83%
public exploits
0
none known

Summary

Windows AD FS Security Feature Bypass Vulnerability

Patch / fix

  • Microsoft Windows Server 2019 10.0.17763.2237
  • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2237
  • Microsoft Windows Server 2022 10.0.20348.288
  • Microsoft Windows Server version 2004 10.0.19041.1288
  • Microsoft Windows Server version 20H2 10.0.19042.1288

Is CVE-2021-40456 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2y ago

Exploit prediction

2.34% chance of exploitation in the next 30 days, higher than 83% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:U/RL:O/RC:C
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:P/I:N/A:N

Affected products

  • Microsoft Windows Server 2019
  • Microsoft Windows Server 2019 (Server Core installation)
  • Microsoft Windows Server 2022
  • Microsoft Windows Server version 2004
  • Microsoft Windows Server version 20H2

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.