Is CVE-2021-3639 in the CISA KEV catalog?

No. CVE-2021-3639 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2021-3639?

CVE-2021-3639 has a CVSS v3 base score of 6.1 (MEDIUM).

What is the EPSS score for CVE-2021-3639?

CVE-2021-3639 has an EPSS score of 0.75% (51th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-3639?

Upgrade libapache2-mod-auth-mellon on debian 11 to 0.17.0-1+deb11u1 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2021-3639

MEDIUM

6.1

CVSS v3

NVD

Description

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.

CWE-601Open Redirect

How to fix

Remediation Available

libapache2-mod-auth-mellonDebian

Fixed in:0.17.0-1+deb11u1CVE-2021-3639

Fixed in:0.18.0-1CVE-2021-3639

libapache2-mod-auth-mellonUbuntu

Fixed in:0.13.1-1ubuntu0.3USN-5069-1

Fixed in:0.16.0-1ubuntu0.1USN-5069-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeChanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploit Intelligence

0.75%probability of exploitation in 30 days

51stpercentile

Moderate risk: more likely to be exploited than 51% of all known CVEs.

References

Patch2

Third-Party Advisory1

bugzilla.redhat.com

Related Vulnerabilities

Other CWE-601 (Open Redirect) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-4123	High	7.6	98%	-	Fix
CVE-2018-11784	Medium	4.3	94%	-	Fix
CVE-2021-22881	Medium	6.1	87%	-	Fix
CVE-2022-45402	Medium	6.1	82%	-	Fix
CVE-2017-1000117	High	8.8	78%	-	Fix
CVE-2019-10098	Medium	6.1	74%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.