CVE-2021-3639: A flaw was found in mod_auth_mellon where it does not sanitize logout URLs properly

Q: How do I fix CVE-2021-3639?

mod auth mellon: upgrade to 0.18.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-3639 being exploited?

CVE-2021-3639 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-3639 affect?

CVE-2021-3639 affects mod auth mellon. Severity is medium (CVSS 6.1). 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 e

Q: How urgent is CVE-2021-3639?

Priority 37/100. No elevated risk signals yet.

Routine

MEDIUM 6.1UPGRADE

CVE-2021-3639 is a medium-severity flaw (CVSS 6.1) affecting mod auth mellon. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.0% (top 36%)
CISA exploited list	No
Weakness	CWE-601
Published	2022-08-22
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: uninett

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-08-22 15:15 UTCPublished CVE record published
2026-06-17 04:05 UTCUpdated Record last modified

uninett mod auth mellon UPGRADE

Affected: < 0.18.0

Fixed in: 0.18.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy mod-auth-mellon || rpm -q mod-auth-mellon || mod-auth-mellon --version

2. UPGRADE to 0.18.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mod-auth-mellon

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mod-auth-mellon

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-3639?

mod auth mellon: upgrade to 0.18.0. Exact commands for each OS are on this page.

Is CVE-2021-3639 being exploited?

CVE-2021-3639 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-3639 affect?

CVE-2021-3639 affects mod auth mellon. Severity is medium (CVSS 6.1). 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 e

How urgent is CVE-2021-3639?

Priority 37/100. No elevated risk signals yet.

References

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