{"id":"CVE-2023-38691","aliases":["GHSA-vc7j-h8xg-fv5x"],"url":"https://o3.security/vulnerability/CVE-2023-38691","summary":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","details":"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.","published":"2023-08-04T16:34:54.312Z","modified":"2026-07-15T01:49:05.117459567Z","cvss":{"score":5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"matrix-appservice-bridge","fixedVersion":"8.1.2"},{"ecosystem":"npm","name":"matrix-appservice-bridge","fixedVersion":"9.0.1"}],"fix":{"url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552","label":"matrix-org/matrix-appservice-bridge@4c6723a"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/38xxx/CVE-2023-38691.json"},{"type":"ADVISORY","url":"https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-38691"},{"type":"FIX","url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-15T01:49:05.117459567Z"}}