Authelia allows open redirects on the logout endpoint

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2021-29456: 0.51% estimated exploitation activity in the next 30 days; percentile 43.56 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Utilizing a HTTP query parameter an attacker is able to redirect users from the web application to any domain. The URL of the intended redirect should always be checked for safety prior to forwarding the user. Other endpoints of the web application already do this, they check both that the domain is using the HTTPS protocol and that it exists on a domain associated with the application. An attacker is able to use this unintended functionality to redirect users to malicious sites. This particular security issue allows the attacker to make a phishing attempt seem much more trustworthy to a user of the web application as the initial site before redirection is familiar to them, as well as the actual URL which they have theoretically visited frequently. While this security issue does not directly impact the security of the web application, it is still not an acceptable scenario for the reasons mentioned above. Patches f0cb75e1e102f95f91e9254c66c797e821857690 fix(handlers): logout…

Published by the source

16 Mar 2023, 16:04 UTC

Last modified by the source

16 Mar 2023, 16:04 UTC

Source last checked

26 Oct 2026, 14:55 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-36f2-fcrx-fp4j

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# Patch Next advisory brief: CVE-2021-29456

Advisory: Authelia allows open redirects on the logout endpoint
IDs: CVE-2021-29456, GHSA-36f2-fcrx-fp4j
Record: https://patchnext.com/advisories/cve-2021-29456 (revision 1, source checked 26 Oct 2026, 14:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/authelia/authelia/v4 4.28.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/authelia/authelia/v4: affected < 4.28.0; fixed in 4.28.0

## Suggested inspection (read-only)
- Go github.com/authelia/authelia/v4: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/authelia/authelia/v4.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-36f2-fcrx-fp4j (GitHub-reviewed advisory GHSA-36f2-fcrx-fp4j lists affected ranges: Go github.com/authelia/authelia/v4 >=0 <4.28.0)

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