Reported by @lauritzh
Given an OAuth2 provider configured with allowed redirect URIs set to
.*, 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.
authentik 2023.8.6 and 2023.10.6 fix this issue.
The impact depends on the attack scenario. In the following I will describe the two scenario that were identified for Authentik.
Redirect URI Misconfiguration
While advising that this may cause security issues, Authentik generally allows wildcards as Redirect URI. Therefore, using a wildcard-only effectively allowing arbitrary URLS is possible misconfiguration that may 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.
It is recommended to upgrade to the patched version of authentik. If not possible, ensure that OAuth2 providers do not use a wildcard (
.*) value as allowed redirect URI setting. (This is not exploitable if part of the redirect URI has a wildcard, for example
For more information
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