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CVE-2021-39191

22
FAUCET Score

CVE-2021-39191 is an open redirect vulnerability affecting mod_auth_openidc versions prior to 2.4.9.4, which is an Apache module for OpenID Connect authentication. This flaw allows an attacker to redirect users to arbitrary malicious sites by manipulating the target_link_uri parameter. With a CVSS score of 6.1 (Medium), the vulnerability requires user interaction and could lead to information disclosure or phishing attacks. There is no evidence of active exploitation, publicly available exploit code, or significant community discussion surrounding this CVE. Upgrading to version 2.4.9.4 or later is the only known remediation.

Impacted Technologies

VendorProductVersion(s)CPE
< 2.4.9.4CPE matchmatch criteria
cpe:2.3:a:openidc:mod_auth_openidc:*:*:*:*:*:*:*:*
35CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
36CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:36:*:*:*:*:*:*:*
10.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

4.7MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.75%
Probability of exploitation in next 30 days
EPSS Percentile
75.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0175 is in the 87th percentile among its peer group of 26,221 CVEs.

Social Chatter

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

Media Mentions

No media coverage found for this CVE.

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 (4)

github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: 18363-16823Fixed in: 2.4.14.2-1
microsoftpatch availablevia msrc
Product: cbl2 mod_auth_openidc 2.4.14.2-1 on CBL Mariner 2.0Fixed in: 2.4.14.2-1
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: mod_auth_openidc:2.3-8060020220131105504.d63f516d
View patch

Vendor Advisories (2)

microsoft2021-Sep/CVE-2021-39191Moderate

URL Redirection to Untrusted Site ('Open Redirect') in mod_auth_openidc

Sep 14, 2021
redhatCVE-2021-39191Moderate

mod_auth_openidc: open redirect due to target_link_uri parameter not validated

Sep 3, 2021

References

github.com / zmartzone/mod_auth_openidc/commit/03e6bfb446f4e3f27c003d30d6a433e5dd8e2b3d
PatchThird Party Advisory
github.com / zmartzone/mod_auth_openidc/issues/672
Exploit
github.com / zmartzone/mod_auth_openidc/releases/tag/v2.4.9.4
Release Notes
github.com / zmartzone/mod_auth_openidc/security/advisories/GHSA-2pgf-8h6h-gqg2
Vendor Advisory
lists.debian.org / debian-lts-announce/2023/07/msg00020.html
Mailing List
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/32RGPW5LZDLDTB7MKZIGAHPSLFOUNWR5
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/RHXO4O4G2UQS7X6OQJCVZKHZAQ7SAIFB