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Fencer Vulns
medium 6.1

CVE-2021-3639 json

A flaw was found in mod_auth_mellon where it does not sanitize logout URLs properly.

published 2022-08-22 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26939

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

A flaw was found in mod_auth_mellon where it does not sanitize logout URLs properly. This issue could be used by an attacker to facilitate phishing attacks by tricking users into visiting a trusted web application URL that redirects to an external and potentially malicious server. The highest threat from this liability is to confidentiality and integrity.

Patch / fix

  • uninett mod_auth_mellon 0.18.0
  • libapache2-mod-auth-mellon Debian 14, Debian 13, Debian 12 0.18.0-1

debian advisories DEBIAN-CVE-2021-3639

  • libapache2-mod-auth-mellon Ubuntu 18.04 LTS 0.13.1-1ubuntu0.3
  • libapache2-mod-auth-mellon Ubuntu 20.04 LTS 0.16.0-1ubuntu0.1
  • libapache2-mod-auth-mellon Ubuntu 22.04 LTS 0.17.0-1ubuntu1

ubuntu advisories UBUNTU-CVE-2021-3639

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • mod_auth_mellon RHEL 8 0.14.0-12.el8.1
  • mod_auth_mellon-diagnostics RHEL 8 0.14.0-12.el8.1

red hat advisories RHSA-2022:1934

  • apache2-mod_auth_mellon SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLES 15 SP2-BCL +10 more 0.17.0-150200.5.7.1
  • apache2-mod_auth_mellon SLES for SAP 12 SP5, SLES 12 SP5 0.16.0-8.6.1

suse advisories SUSE-SU-2022:1524-1SUSE-SU-2021:2912-1

  • apache2-mod_auth_mellon openSUSE Tumbleweed 0.19.0-1.1

opensuse advisories openSUSE-SU-2024:13848-1

  • mod_auth_mellon AlmaLinux 8 0.14.0-12.el8.1
  • mod_auth_mellon-diagnostics AlmaLinux 8 0.14.0-12.el8.1

almalinux advisories ALSA-2022:1934

  • mod_auth_mellon Rocky Linux 8 0.14.0-12.el8.1

rocky linux advisories RLSA-2022:1934

  • mod_auth_mellon CBL-Mariner 2.0, Azure Linux 3.0 0.16.0-4

azure linux advisories AZL-10651AZL-36962

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-2021-3639 updated cvss 6.1

mod_auth_mellon: Open Redirect vulnerability in logout URLs

  • Red Hat Enterprise Linux 6 mod_auth_mellon Red Hat Enterprise Linux 7 mod_auth_mellon, mod_auth_mellon-diagnostics
    affected: no fix planned “Out of support scope”
  • Red Hat Software Collections httpd24-mod_auth_mellon
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux AppStream (v. 8) mod_auth_mellon 0.14.0-12.el8.1, mod_auth_mellon-diagnostics 0.14.0-12.el8.1
    fixed: vendor fix RHSA-2022:1934
  • Red Hat Enterprise Linux 9 mod_auth_mellon, mod_auth_mellon-diagnostics
    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

1.06% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected products

  • n/a mod_auth_mellon

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.