This fixes a vulnerability where an attacker with a malicious remote
server and a user on the local server can trick the local server into
signing arbitrary events. The attacker issue a remote leave as the local
user to a room on the malicious server. Without any validation of the
make_leave response, the local server would sign the attacker-controlled
event and pass it back to the malicious server with send_leave.
The join and knock endpoints are also fixed in this commit, but are less
useful for exploitation because the local server replaces the "content"
field returned by the remote server. Remote invites are unaffected
because we already check that the event returned from /invite has the
same event ID as the event passed to it.
Co-authored-by: timedout <git@nexy7574.co.uk>
Co-authored-by: Jade Ellis <jade@ellis.link>
Co-authored-by: Ginger <ginger@gingershaped.computer>
**Does not yet work!** Currently, state resolution does not correctly resolve conflicting states. Everything else appears to work as expected, so stateres will be fixed soon, then we should be clear for takeoff.
Also: a lot of things currently accept a nullable room ID that really just don't need to. This will need tidying up before merge. Some authentication checks have also been disabled temporarily but nothing important.
A lot of things are tagged with `TODO(hydra)`, those need resolving before merge. External contributors should PR to the `hydra/public` branch, *not* ` main`.
---
This PR should be squash merged.
Reviewed-on: https://forgejo.ellis.link/continuwuation/continuwuity/pulls/943
Co-authored-by: nexy7574 <git@nexy7574.co.uk>
Co-committed-by: nexy7574 <git@nexy7574.co.uk>
