Affected: Homebrew: ggshield

The security of both a TUF client and repository implementations depend on the concept of trusted Metadata objects verifying the signatures over other Metadata that it delegates to. This verification process uses `Targets.get_delegated_role(delegated_role: str)` to find the delegation information.

`tuf.api.metadata.Targets.get_delegated_role()` should ensure that the given `delegated_rolename` is actually a name of a role that is delegated by that Targets, but in the case of "succinct delegation" this does not happen.

`tuf.ngclient` users are **not** impacted but direct users of `tuf.api.metadata` could be impacted.

### Impact

If an attacker can make a Metadata API user run `Targets.get_delegated_role()` so that 1. the `Targets` uses succinct delegation 1. the `delegated_role` argument is not actually delegated by the `Targets`

the result will be incorrect.

This also means that if an attacker can make a Metadata API user run `Targets.verify_delegate()` or `Targets.get_verification_result()` so that 1. the delegating `Targets` uses a succinct delegation 1. the `delegated_role` argument is the name of some unrelated Metadata 1. that other Metadata is correctly signed by the keys defined in the succinct delegation

the result would be a successful verification even though the `Targets` in question does not actually delegate to `delegated_role`.

The impact is estimated to be low for following reasons:

* This cannot impact a TUF client that implements the client workflow…