Skip to content
Fencer Vulns
medium 4.7

CVE-2021-39191 json

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

published 2021-09-03 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-25579

cvss
4.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

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.

Patch / fix

  • openidc mod_auth_openidc 2.4.9.4
  • libapache2-mod-auth-openidc Debian 14, Debian 13, Debian 12 2.4.9.4-1

debian advisories DEBIAN-CVE-2021-39191

  • cjose RHEL 8 0.6.1-2.module+el8+2454+f890a43a
  • mod_auth_openidc RHEL 8 2.3.7-11.module+el8.6.0+14082+b6f23e95

red hat advisories RHSA-2022:1823

  • apache2-mod_auth_openidc SLE Module for Server Applications 15 SP7, SLE Module for Server Applications 15 SP6, openSUSE Leap 15.6 2.4.17.1-150600.16.14.1
  • apache2-mod_auth_openidc SLE Real Time 15 SP3, SLE Module for Server Applications 15 SP4, openSUSE Leap 15.4 2.3.8-150100.3.22.1
  • apache2-mod_auth_openidc SLES for SAP 12 SP5, SLES 12 SP5 2.4.0-3.23.1

suse advisories SUSE-SU-2025:4532-1SUSE-SU-2023:0215-1SUSE-SU-2021:3352-1

  • cjose AlmaLinux 8 0.6.1-2.module_el8.6.0+2868+44838709
  • mod_auth_openidc AlmaLinux 8 2.3.7-11.module_el8.6.0+2868+44838709

almalinux advisories ALSA-2022:1823

  • cjose Rocky Linux 8 0.6.1-2.module+el8.3.0+129+2feafa46
  • mod_auth_openidc Rocky Linux 8 2.3.7-11.module+el8.6.0+840+73eca44e

rocky linux advisories RLSA-2022:1823

  • mod_auth_openidc CBL-Mariner 2.0 2.4.14.2-1

azure linux advisories AZL-7289

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-39191 updated cvss 6.1

mod_auth_openidc: open redirect due to target_link_uri parameter not validated

  • Red Hat Enterprise Linux 7 mod_auth_openidc
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) cjose 0.6.1-2.module+el8+2454+f890a43a, mod_auth_openidc 2.3.7-11.module+el8.6.0+14082+b6f23e95
    fixed: vendor fix RHSA-2022:1823
  • Red Hat Enterprise Linux 9 mod_auth_openidc
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.74% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/zmartzone/mod_auth_openidc/issues/672 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N

Affected products

  • zmartzone mod_auth_openidc

Classification

Weakness
  • CWE-601 URL Redirection to Untrusted Site

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.