CVE-2021-29456: Authelia allows open redirects on the logout endpoint

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-04-21 · updated 2026-06-17
Weakness: CWE-601

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.

Affected products

authelia: before 4.28.0 — fixed in 4.28.0

How to fix

Upgrade to a fixed version: authelia 4.28.0. Check the vendor advisory for mitigations.

References

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