What’s Vulnerable › Vulnerabilities
CVE-2021-39191: URL Redirection to Untrusted Site ('Open Redirect') in mod_auth_openidc
- Severity: medium (CVSS 6.1 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.7% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2021-09-03 · updated 2026-06-17
- Weakness: CWE-601
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.
Affected products
- Debian Linux: 10.0
- Fedoraproject Fedora: 35, 36
- OpenIDC mod_auth_openidc: before 2.4.9.4 — fixed in 2.4.9.4
How to fix
Upgrade to a fixed version: OpenIDC mod_auth_openidc 2.4.9.4. Check the vendor advisory for mitigations.
References
- https://github.com/zmartzone/mod_auth_openidc/commit/03e6bfb446f4e3f27c003d30d6a433e5dd8e2b3d
- https://github.com/zmartzone/mod_auth_openidc/issues/672
- https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9.4
- https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-2pgf-8h6h-gqg2
- https://lists.debian.org/debian-lts-announce/2023/07/msg00020.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/32RGPW5LZDLDTB7MKZIGAHPSLFOUNWR5/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RHXO4O4G2UQS7X6OQJCVZKHZAQ7SAIFB/
- https://github.com/zmartzone/mod_auth_openidc/commit/03e6bfb446f4e3f27c003d30d6a433e5dd8e2b3d
- https://github.com/zmartzone/mod_auth_openidc/issues/672
- https://github.com/zmartzone/mod_auth_openidc/releases/tag/v2.4.9.4
- https://github.com/zmartzone/mod_auth_openidc/security/advisories/GHSA-2pgf-8h6h-gqg2
- https://lists.debian.org/debian-lts-announce/2023/07/msg00020.html
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