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CVE-2024-21637

Reported by @lauritzh

XSS in authentik via JavaScript URI as redirect URI and form_post response mode​

Summary​

Given an OAuth2 provider configured with allowed redirect URIs set to * or .*, an attacker can send an OAuth Authorization request using response_mode=form_post and setting redirect_uri to a malicious URI, to capture authentik's session token.

Patches​

authentik 2023.8.6 and 2023.10.6 fix this issue.

Impact​

The impact depends on the attack scenario. The following sections describe the two scenarios that were identified for authentik.

Redirect URI misconfiguration​

Although authentik advises that this can cause security issues, authentik generally allows wildcards as redirect URIs. Therefore, using only a wildcard and effectively allowing arbitrary URLs is a possible misconfiguration that can be present in real-world instances.

In such cases, unauthenticated and unprivileged attackers can perform the above described actions.

User with (only) App Administration Permissions​

A more likely scenario is an administrative user (e.g. a normal developer) having only permissions to manage applications.

This relatively user could use the described attacks to perform a privilege escalation.

Workaround​

It is recommended to upgrade to the patched version of authentik. If not possible, ensure that OAuth2 providers do not use a wildcard (* or .*) value as allowed redirect URI setting. (This is not exploitable if part of the redirect URI has a wildcard, for example https://foo-.*\.bar\.com)

For more information​

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