## Token reuse in invitation URLs leads to access control bypass via the use of a different enrollment flow
### Summary
Token reuse in invitation URLs leads to access control bypass via the use of a different enrollment flow than in the one provided.
### Patches
authentik 2022.11.4, 2022.10.4 and 2022.12.0 fix this issue, for other versions the workaround can be used.
### Impact
Only configurations using both invitations and have multiple enrollment flows with invitation stages that grant different permissions are affected. The default configuration is not vulnerable, and neither are configurations with a single enrollment flow.
### Details
The vulnerability allows an attacker that knows different invitation flows names (e.g. `enrollment-invitation-test` and `enrollment-invitation-admin`) via either different invite links or via brute forcing to signup via a single invitation url for any valid invite link received (it can even be a url for a third flow as long as it's a valid invite) as the token used in the `Invitations` section of the Admin interface does NOT change when a different `enrollment flow` is selected via the interface and it is NOT bound to the selected flow, so it will be valid for any flow when used.
### Workarounds
As a workaround, fixed data can be added to invitations which can be checked in the flow to deny requests. Alternatively, an identifier with high entropy (like a UUID) can be used as flow slug, mitigating the attack vector by exponentially decreasing the possibility of discovering other flows.
### For more information
If you have any questions or comments about this advisory:
- Email us at [security@goauthentik.io](mailto:security@goauthentik.io)
