authentik is an open-source identity provider. Redirect URIs in the OAuth2 provider in authentik are checked by RegEx comparison. When no Redirect URIs are configured in a provider, authentik will automatically use the first redirect_uri value received as an allowed redirect URI, without escaping characters that have a special meaning in RegEx. Similarly, the documentation did not take this into consideration either. Given a provider with the Redirect URIs set to https://foo.example.com, an attacker can register a domain fooaexample.com, and it will correctly pass validation. authentik 2024.8.5 and 2024.10.3 fix this issue. As a workaround, When configuring OAuth2 providers, make sure to escape any wildcard characters that are not intended to function as a wildcard, for example replace "." with "\.".