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CVE-2021-33779

26
FAUCET Score

CVE-2021-33779 is a high-severity security feature bypass vulnerability affecting Microsoft Windows Server 2016 and 2019's Active Directory Federation Services (AD FS). With a CVSS score of 8.1, it allows a low-privileged attacker to achieve high confidentiality and integrity impacts over the network without user interaction. While there is no public exploit code (Metasploit, Nuclei, ExploitDB) and it's not listed in CISA's KEV catalog, the vulnerability has garnered significant community discussion and media coverage, indicating notable attention from security researchers. Microsoft has released patches to address this flaw.

Impacted Technologies

VendorProductVersion(s)CPE
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_2016:-:*:*:*:*:*:*:*
20h2CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_2016:20h2:*:*:*:*:*:*:*
2004CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_2016:2004:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_2019:-:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.1HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
5.2
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.23%
Probability of exploitation in next 30 days
EPSS Percentile
80.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0223 is in the 79th percentile among its peer group of 17,844 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.3 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (7)

microsoftpatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: Windows Server 2019Fixed in: 10.0.17763.2061
View patch
microsoftpatch availablevia msrc
Product: Windows Server 2019 (Server Core installation)Fixed in: 10.0.17763.2061
View patch
microsoftpatch availablevia msrc
Product: Windows Server, version 2004 (Server Core installation)Fixed in: 10.0.19041.1110
View patch
microsoftpatch availablevia msrc
Product: Windows Server, version 20H2 (Server Core Installation)Fixed in: 10.0.19042.1110
View patch
microsoftpatch availablevia msrc
Product: Windows Server 2016Fixed in: 10.0.14393.4530
View patch
microsoftpatch availablevia msrc
Product: Windows Server 2016 (Server Core installation)Fixed in: 10.0.14393.4530
View patch

Vendor Advisories (1)

microsoft2021-Jul/CVE-2021-33779Important

Windows AD FS Security Feature Bypass Vulnerability

Jul 13, 2021

References

portal.msrc.microsoft.com / en-US/security-guidance/advisory/CVE-2021-33779
PatchVendor Advisory