{"id":"GHSA-vc7j-h8xg-fv5x","summary":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","details":"### Impact\n\nA 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.\n\n### Details\n\nThe 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.\n\n### Workarounds\n\nDisable the provisioning API. If the bridge does not use the provisioning API, you are not vulnerable.\n","aliases":["CVE-2023-38691"],"modified":"2026-09-10T03:49:57.718797886Z","published":"2023-08-04T17:26:32Z","database_specific":{"nvd_published_at":"2023-08-04T17:15:11Z","cwe_ids":["CWE-287"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2023-08-04T17:26:32Z"},"references":[{"type":"WEB","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":"WEB","url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552"},{"type":"PACKAGE","url":"https://github.com/matrix-org/matrix-appservice-bridge"}],"affected":[{"package":{"name":"matrix-appservice-bridge","ecosystem":"npm","purl":"pkg:npm/matrix-appservice-bridge"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"8.1.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/08/GHSA-vc7j-h8xg-fv5x/GHSA-vc7j-h8xg-fv5x.json"}},{"package":{"name":"matrix-appservice-bridge","ecosystem":"npm","purl":"pkg:npm/matrix-appservice-bridge"},"ranges":[{"type":"SEMVER","events":[{"introduced":"9.0.0"},{"fixed":"9.0.1"}]}],"versions":["9.0.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/08/GHSA-vc7j-h8xg-fv5x/GHSA-vc7j-h8xg-fv5x.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N"}]}