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CVE-2021-3639

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

6.1 MediumFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Required

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

1.03%Up 0.1 points since Aug 23, 2022
90%50%10%1%

What each source reports

NVD Score used 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 external and potentially malicious server. The highest threat from this liability is to confidentiality and integrity.

Record
CVE-2021-3639
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-601
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2021-3639
Weakness
CWE-601
Updated
2026-11-02
EUVDEUVD-2021-26939 No score

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.

Record
EUVD-2021-26939
Updated
2026-11-03
GitHub AdvisoriesGHSA-mhcv-7w89-jjj5 6.1

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

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.

Record
GHSA-mhcv-7w89-jjj5
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness
CWE-601
Updated
2026-11-02
OSVAZL-10651 6.1

CVE-2021-3639 affecting package mod_auth_mellon for versions less than 0.16.0-4

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.

Record
AZL-10651
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVAZL-36962 6.1

CVE-2021-3639 affecting package mod_auth_mellon for versions less than 0.16.0-4

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.

Record
AZL-36962
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-05
Show 10 moreShow less
OSV 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 external and potentially malicious server. The highest threat from this liability is to confidentiality and integrity.

Record
CVE-2021-3639
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2021-3639 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 external and potentially malicious server. The highest threat from this liability is to confidentiality and integrity.

Record
DEBIAN-CVE-2021-3639
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVRHSA-2022:1934 6.1

Red Hat Security Advisory: mod_auth_mellon security update

Record
RHSA-2022:1934
CVSS 3.0
6.1 MediumCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVRLSA-2022:1934 6.1

Moderate: mod_auth_mellon security update

The mod_auth_mellon module for the Apache HTTP Server is an authentication service that implements the SAML 2.0 federation protocol. The module grants access based on the attributes received in assertions generated by an IdP server.

Security Fix(es):

  • mod_auth_mellon: Open Redirect vulnerability in logout URLs (CVE-2021-3639)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the Rocky Linux 8.6 Release Notes linked from the References section.

Record
RLSA-2022:1934
CVSS 3.0
6.1 MediumCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2021-3639 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 external and potentially malicious server. The highest threat from this liability is to confidentiality and integrity.

Record
UBUNTU-CVE-2021-3639
CVSS 3.1
6.1 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVALSA-2022:1934 No score

Moderate: mod_auth_mellon security update

The mod_auth_mellon module for the Apache HTTP Server is an authentication service that implements the SAML 2.0 federation protocol. The module grants access based on the attributes received in assertions generated by an IdP server.

Security Fix(es):

  • mod_auth_mellon: Open Redirect vulnerability in logout URLs (CVE-2021-3639)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the AlmaLinux Release Notes linked from the References section.

Record
ALSA-2022:1934
Updated
2026-11-02
OSVopenSUSE-SU-2024:13848-1 No score

apache2-mod_auth_mellon-0.19.0-1.1 on GA media

These are all security issues fixed in the apache2-mod_auth_mellon-0.19.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:13848-1
Updated
2026-11-02
OSVSUSE-SU-2021:2912-1 No score

Security update for apache2-mod_auth_mellon

This update for apache2-mod_auth_mellon fixes the following issues:

  • CVE-2021-3639: Fixed Open Redirect vulnerability in logout URLs (bsc#1188926).
Record
SUSE-SU-2021:2912-1
Updated
2026-11-02
OSVSUSE-SU-2022:1524-1 No score

Security update for apache2-mod_auth_mellon

This update for apache2-mod_auth_mellon fixes the following issues:

  • CVE-2021-3639: Fixed open Redirect vulnerability in logout URLs (bsc#1188926)
Record
SUSE-SU-2022:1524-1
Updated
2026-11-02
OSVUSN-5069-1 No score

libapache2-mod-auth-mellon vulnerability

It was discovered that mod-auth-mellon incorrectly filtered certain URLs. A remote attacker could possibly use this issue to perform an open redirect attack.

Record
USN-5069-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mod_auth_mellon
AlmaLinux:8
before 0.14.0-12.el8.1
0.14.0-12.el8.1
mod_auth_mellon-diagnostics
AlmaLinux:8
before 0.14.0-12.el8.1
0.14.0-12.el8.1
mod_auth_mellon
Azure Linux:2
before 0.16.0-4
0.16.0-4
mod_auth_mellon
Azure Linux:3
before 0.16.0-4
0.16.0-4
libapache2-mod-auth-mellon
Debian:12
before 0.18.0-1
0.18.0-1
libapache2-mod-auth-mellon
Debian:13
before 0.18.0-1
0.18.0-1
libapache2-mod-auth-mellon
Debian:14
before 0.18.0-1
0.18.0-1
libapache2-mod-auth-mellon
Debian:10
From an advisory covering 2 CVEs
before 0.14.2-1+deb10u1, plus listed versions
0.14.2-1
0.14.2-1+deb10u1
mod_auth_mellon
Red Hat:enterprise_linux:8::appstream
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
mod_auth_mellon-debuginfo
Red Hat:enterprise_linux:8::appstream
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
Show 24 moreShow less
Affected packages
PackageAffectedFixed
mod_auth_mellon-debugsource
Red Hat:enterprise_linux:8::appstream
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
mod_auth_mellon-diagnostics
Red Hat:enterprise_linux:8::appstream
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
mod_auth_mellon-diagnostics-debuginfo
Red Hat:enterprise_linux:8::appstream
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
mod_auth_mellon
Rocky Linux:8
before 0:0.14.0-12.el8.1
0:0.14.0-12.el8.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Server 12 SP5
before 0.16.0-8.6.1
0.16.0-8.6.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Server for SAP Applications 12 SP5
before 0.16.0-8.6.1
0.16.0-8.6.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Module for Server Applications 15 SP3
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise High Performance Computing 15 SP2-ESPOS
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise High Performance Computing 15 SP2-LTSS
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Real Time 15 SP2
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Server 15 SP2-BCL
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Server 15 SP2-LTSS
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Linux Enterprise Server for SAP Applications 15 SP2
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Manager Proxy 4.1
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Manager Retail Branch Server 4.1
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Manager Server 4.1
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
SUSE:Enterprise Storage 7
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
openSUSE:Leap 15.3
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
apache2-mod_auth_mellon
openSUSE:Leap 15.4
before 0.17.0-150200.5.7.1
0.17.0-150200.5.7.1
libapache2-mod-auth-mellon
Ubuntu:16.04:LTS
All versions, plus listed versions
0.10.0-10.11.0-10.12.0-10.12.0-2+deb9u1build0.16.04.1
None known
libapache2-mod-auth-mellon
Ubuntu:18.04:LTS
before 0.13.1-1ubuntu0.3, plus listed versions
0.13.1-10.13.1-1build10.13.1-1build20.13.1-1ubuntu0.10.13.1-1ubuntu0.2
0.13.1-1ubuntu0.3
libapache2-mod-auth-mellon
Ubuntu:20.04:LTS
before 0.16.0-1ubuntu0.1, plus listed versions
0.14.2-1ubuntu10.14.2-1ubuntu20.16.0-1
0.16.0-1ubuntu0.1
libapache2-mod-auth-mellon
Ubuntu:22.04:LTS
before 0.17.0-1ubuntu1
0.17.0-1ubuntu1
apache2-mod_auth_mellon
openSUSE:Tumbleweed
before 0.19.0-1.1
0.19.0-1.1

History

History
RecordedChangedSources
affected
factsOSV
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-3639 is a medium vulnerability (CVSS 6.1) in Uninett Mod Auth Mellon, published August 4, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.03%, the 63rd percentile. Fixed in mod_auth_mellon 0.14.0-12.el8.1.

References

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