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Fencer Vulns
medium 4.7

CVE-2021-32786 json

Open Redirect in oidc_validate_redirect_url()

published 2021-07-22 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-19549

cvss
4.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.4%
EPSS 2.4% chance of exploitation in 30 days, percentile 83%
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, `oidc_validate_redirect_url()` does not parse URLs the same way as most browsers do. As a result, this function can be bypassed and leads to an Open Redirect vulnerability in the logout functionality. This bug has been fixed in version 2.4.9 by replacing any backslash of the URL to redirect with slashes to address a particular breaking change between the different specifications (RFC2396 / RFC3986 and WHATWG). As a workaround, this vulnerability can be mitigated by configuring `mod_auth_openidc` to only allow redirection whose destination matches a given regular expression.

Patch / fix

  • openidc mod_auth_openidc 2.4.9
  • libapache2-mod-auth-openidc Debian 14, Debian 13, Debian 12 2.4.9-1

debian advisories DEBIAN-CVE-2021-32786

  • 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 SLES for SAP 12 SP5, SLES 12 SP5 2.4.0-3.23.1
  • apache2-mod_auth_openidc SLE Module for Server Applications 15 SP3, SLE Module for Server Applications 15 SP2 2.3.8-3.15.1

suse advisories SUSE-SU-2025:4532-1SUSE-SU-2021:3352-1SUSE-SU-2021:3020-1

  • apache2-mod_auth_openidc openSUSE Tumbleweed 2.4.9.4-1.2
  • apache2-mod_auth_openidc openSUSE Leap 15.2 2.3.8-lp152.5.6.1
  • apache2-mod_auth_openidc openSUSE Leap 15.3 2.3.8-3.15.1

opensuse advisories openSUSE-SU-2024:10624-1openSUSE-SU-2021:1277-1openSUSE-SU-2021:3020-1

  • 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

  • httpd CBL-Mariner 2.0 2.4.52-1

azure linux advisories AZL-6480

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-2021-32786 updated cvss 6.1

mod_auth_openidc: open redirect in oidc_validate_redirect_url()

  • 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

2.36% chance of exploitation in the next 30 days, higher than 83% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • daniel.haxx.se https://daniel.haxx.se/blog/2017/01/30/one-url-standard-please/ 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.