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EUVD-2026-193073

2026-10-17T18:08:08.871920+00:00

EUVD-2026-193073

fkie_cve-2023-38691

2026-10-17T18:08:08.871950+00:00

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.

GHSA-vc7j-h8xg-fv5x — matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to p…

2026-10-17T18:08:08.872027+00:00

Affected: npm: matrix-appservice-bridge

### 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.

gsd-2023-38691

2026-10-17T18:08:08.872079+00:00

gsd-2023-38691