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

What is CVE-2021-29456?

CVE-2021-29456 is a medium-severity vulnerability in authelia, published on 21 Apr 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-601

Which versions are affected by CVE-2021-29456?

2 open source packages ship an affected version, including github.com/authelia/authelia/v4. It affects 1 product.

Products include Authelia Authelia.

How do I fix CVE-2021-29456?

Upgrade github.com/authelia/authelia/v4 to 4.28.0 or later.

Is CVE-2021-29456 being exploited?

There is no known exploitation of CVE-2021-29456 in the wild and no public exploit code.

Other vulnerabilities in authelia

• CVE-2021-32637 Authentication bypassed with malformed request URI Critical 10.0
• CVE-2026-33525 Authelia: Improper Neutralization of Input During Web Page Generation Leads to Potential Cross-site Scripting Low 0.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-36f2-fcrx-fp4j.