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Vulnerability record · CVE-2021-39191 · published 3 September 2021

CVE-2021-39191: Mod auth openidc open redirect vulnerability

Openidc · Mod Auth Openidc

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 the `OIDCRedirectURLsAllowed` setting must be applied to the `target_link_uri` parameter. There are no known workarounds aside from upgrading to a patched version.

6.1 CVSS 3.1 Medium EPSS 1.7% · top 23.2% CWE-601 · Open redirect
6.1CVSS 3.1 base score, v2 5.8
1.7%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
14References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

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 the `OIDCRedirectURLsAllowed` setting must be applied to the `target_link_uri` parameter. There are no known workarounds aside from upgrading to a patched version.

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

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/zmartzone/mod_auth_openidc/commit/03e6bfb446f4e3f27c003d30d6a433e5dd8e2b3d PatchThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/issues/672 Exploit
https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9.4 Release Notes
https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-2pgf-8h6h-gqg2 Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/07/msg00020.html Mailing List
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/32RGPW5LZDLDTB7MKZIGAHP
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RHXO4O4G2UQS7X6OQJCVZKH
https://github.com/zmartzone/mod_auth_openidc/commit/03e6bfb446f4e3f27c003d30d6a433e5dd8e2b3d PatchThird Party Advisory
https://github.com/zmartzone/mod_auth_openidc/issues/672 Exploit
https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9.4 Release Notes
https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-2pgf-8h6h-gqg2 Vendor Advisory
https://lists.debian.org/debian-lts-announce/2023/07/msg00020.html Mailing List
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/32RGPW5LZDLDTB7MKZIGAHP
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RHXO4O4G2UQS7X6OQJCVZKH

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Source: NIST National Vulnerability Database (record CVE-2021-39191), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.