### Impact
A malicious Matrix server can use a foreign user’s MXID in an OpenID exchange, allowing a bad actor to impersonate users when using the provisioning API.
### Details
The library does not check that the servername part of the `sub` parameter (containing the user’s *claimed* MXID) is the same as the servername we are talking to. A malicious actor could spin up a server on any given domain, respond with a `sub` parameter according to the user they want to act as and use the resulting token to perform provisioning requests.
### Workarounds
Disable the provisioning API. If the bridge does not use the provisioning API, you are not vulnerable.Read More