CVE-2021-39191: mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an

Q: How do I fix CVE-2021-39191?

mod auth openidc: upgrade to 2.4.9.4; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-39191 being exploited?

CVE-2021-39191 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-39191 affect?

CVE-2021-39191 affects mod auth openidc, fedora, debian linux. Severity is medium (CVSS 4.7). mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. In versions prior to 2.4.9.4, the 3rd-part

Q: How urgent is CVE-2021-39191?

Priority 46/100. Public exploit reference; On your watchlist

This month

MEDIUM 4.7WATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-39191 is a medium-severity flaw (CVSS 4.7) affecting mod auth openidc, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. In versions prior to 2.4.9.4, the 3rd-party init SSO functionality of mod_auth_openidc was reported to be vulnerable to an open redirect attack by supplying a crafted URL in the `target_link_uri` parameter. A patch in version 2.4.9.4 made it so that th

Why this priority

Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	4.7 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.7% (top 22%)
CISA exploited list	No
Weakness	CWE-601
Published	2021-09-03
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: debian · fedoraproject · openidc

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-09-03 14:15 UTCPublished CVE record published
2026-06-17 04:03 UTCUpdated Record last modified

openidc mod auth openidc UPGRADE

Affected: < 2.4.9.4

Fixed in: 2.4.9.4

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mod-auth-openidc || rpm -q mod-auth-openidc || mod-auth-openidc --version

2. UPGRADE to 2.4.9.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mod-auth-openidc

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mod-auth-openidc

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 35 · 36

Fixed in: no fixed release known

Safe to downgrade to: a release before 35

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-39191?

mod auth openidc: upgrade to 2.4.9.4; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-39191 being exploited?

CVE-2021-39191 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-39191 affect?

CVE-2021-39191 affects mod auth openidc, fedora, debian linux. Severity is medium (CVSS 4.7). mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an OpenID Connect Relying Party, authenticating users against an OpenID Connect Provider. In versions prior to 2.4.9.4, the 3rd-part

How urgent is CVE-2021-39191?

Priority 46/100. Public exploit reference; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2024-24814 HIGH 7.5 UPGRADE MITIGATE mod_auth_openidc is an OpenID Certified™ authentication and authorization module for the Apache 2.x HTTP serve
CVE-2023-28625 HIGH 7.5 UPGRADE mod_auth_openidc is an authentication and authorization module for the Apache 2.x HTTP server that implements
CVE-2022-23527 MEDIUM 4.7 UPGRADE MITIGATE mod_auth_openidc is an OpenID Certified™ authentication and authorization module for the Apache 2.x HTTP serve
CVE-2021-32792 LOW 3.1 UPGRADE MITIGATE mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an
CVE-2021-32791 MEDIUM 5.9 UPGRADE MITIGATE mod_auth_openidc is an authentication/authorization module for the Apache 2.x HTTP server that functions as an

References

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