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No exploitation reportedFix available

CVE-2021-29456

No exploitation reported by the sources we read.

  • Published2021-04-21
  • Fixed in4.28.0
  • WeaknessCWE-601

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Authelia is an open-source authentication and authorization server providing 2-factor authentication and single sign-on (SSO) for your applications via a web portal. In versions 4.27.4 and earlier, utilizing a HTTP query parameter an attacker is able to redirect users from the web application to any domain, including potentially malicious sites. This security issue does not directly impact the security of the web application itself. As a workaround, one can use a reverse proxy to strip the query parameter from the affected endpoint. There is a patch for version 4.28.0.

Timeline

dates in UTC
  1. 2021-04-2119:15CVE publishedNVD

Versions per branch

NVD · OSV
Authelia
BranchAffectedFixed in
4.28< 4.28.04.28.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Authelia to 4.28.0

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.15.7known since 2026-10-23
  • NVDCVSS 3.15.4read 2026-10-23
  • NVDCVSS 2.04.9read 2026-10-23
  • CNAweakness (CWE)CWE-601known since 2026-10-23
  • FIRST EPSSEPSS score0.5 %2026-11-08
  • OSVaffected packages—
  • GitHub AdvisoriesadvisoryMODERATE2023-03-16

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Published
2021-04-21
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-36f2-fcrx-fp4j

Frequently asked questions

What is CVE-2021-29456?

Authelia is an open-source authentication and authorization server providing 2-factor authentication and single sign-on (SSO) for your applications via a web portal. In versions 4.27.4 and earlier, utilizing a HTTP query parameter an attacker is able to redirect users from the web application to any domain, including potentially malicious sites. This security issue does not directly impact the security of the web application itself. As a workaround, one can use a reverse proxy to strip the query parameter from the affected endpoint. There is a patch for version 4.28.0.

Is CVE-2021-29456 actively exploited?

Active exploitation of CVE-2021-29456 has not been confirmed. Its EPSS score was 0.5% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-29456?

CVE-2021-29456 has a CVSS v3 base score of 5.4 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

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