CVE-2021-3639

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.

Published: 2022-08-22 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3639 is rated Moderate Risk (48/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.50%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3639

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-10 0.16% 0.50% +0.34%
2 2026-01-27 0.13% 0.16% +0.03%
3 2025-11-21 — 0.13% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3639

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]

Weakness enumeration for CVE-2021-3639

OS Trackers for CVE-2021-3639

vendor priority summary link
debian not yet assigned CVE-2021-3639 not yet assigned priority: Debian including 1 source packages (libapache2-mod-auth-mellon), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3639
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3639
suse medium CVE-2021-3639 severity moderate: SUSE including 15 source package names (apache2-mod_auth_mellon-0.16.0-8.6.1, apache2-mod_auth_mellon-0.17.0-150200.5.7.1, …), 38 product×package rows across 21 product lines (SUSE Enterprise Storage 7, SUSE Liberty Linux 8, … (21 product lines)): Fixed 38. https://www.suse.com/security/cve/CVE-2021-3639/
ubuntu medium CVE-2021-3639 medium priority: Ubuntu including 1 source packages (libapache2-mod-auth-mellon), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 12, DNE 1, needed 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-3639

Affected software / configurations for CVE-2021-3639

Vendor Product Version Raw CPE
uninett mod_auth_mellon < 0.18.0 cpe:2.3:a:uninett:mod_auth_mellon:*:*:*:*:*:*:*:*

References for CVE-2021-3639

cvelogic Threat Intelligence