CVE-2019-1126 — ADFS Security Feature Bypass Vulnerability

Executive Summary

A security feature bypass vulnerability exists in Active Directory Federation Services (ADFS) which could allow an attacker to bypass the extranet lockout policy. To exploit this vulnerability, an attacker could run a specially crafted application, which would allow an attacker to launch a password brute-force attack or cause account lockouts in Active Directory. This security update corrects how ADFS handles external authentication requests.

Overview

5.3

CVSS MEDIUM

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Security Feature Bypass

Released Jul 9 2019

Last Updated Jul 9 2019

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.04948 — 0.91256 percentile

NVD CVSS 5.3 MEDIUM — matches MSRC

CVSS Vector

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C

ATTACK VECTOR

Network

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

Low

INTEGRITY

None

AVAILABILITY

None

EXPLOIT CODE MATURITY

Proof-of-Concept

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 4.8

EPSS Score

0.04948

probability of exploitation in the next 30 days

0.91256 percentile - updated 2026-07-25

View on FIRST.org

Affected Products

6 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows Server 2012 R2 4507448 (Monthly Rollup) 4507457 (Security Only) Important Security Feature Bypass 4503276 Base: 5.3 Temporal: 4.8 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C Yes None Windows Server 2012 R2 (Server Core installation) 4507448 (Monthly Rollup) 4507457 (Security Only) Important Security Feature Bypass 4503276 Base: 5.3 Temporal: 4.8 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C Yes None Windows Server 2016	`4507460 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2016 (Server Core installation)	`4507460 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2019	`4507469 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server 2019 (Server Core installation)	`4507469 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server, version 1803 (Server Core Installation)	`4507435 (Security Update)`	Important	Security Feature Bypass	Yes
Windows Server, version 1903 (Server Core installation)	`4507453 (Security Update)`	Important	Security Feature Bypass	Yes

Patches

4 patches

Article	Type	Restart
`4507460`	Security Update	Yes
`4507469`	Security Update	Yes
`4507435`	Security Update	Yes
`4507453`	Security Update	Yes

Known Exploits

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

Eyal Karni, Marina Simakov and Yaron Zinar from Preempt

References

MSRC Advisory MITRE NVD