CVE-2023-38691 Information

Description

matrix-appservice-bridge provides an API for setting up bridges. Starting in version 4.0.0 and prior to versions 8.1.2 and 9.0.1 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. The library does not check that the servername part of the sub parameter (containing the user’s claimed MXID) is the 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. Versions 8.1.2 and 9.0.1 contain a patch. As a workaround disable the provisioning API.

Reference

https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552 https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x