{"id":"CVE-2023-38691","aliases":["EUVD-2023-2361","GHSA-vc7j-h8xg-fv5x"],"status":"published","title":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","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.","severity":{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00466,"percentile":0.40762,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-287"],"published":"2023-08-04T16:34:54Z","modified":"2026-10-28T02:30:38Z","fixes":[{"ecosystem":"npm","package":"matrix-appservice-bridge","fixed_in":["8.1.2","9.0.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.0.0"},{"fixed":"8.1.2"}]}]},{"source":"ghsa","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"9.0.0"},{"last_affected":"9.0.0"},{"fixed":"9.0.1"}]}],"versions":["9.0.0"]},{"source":"osv","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"8.1.2"}]}]},{"source":"osv","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"SEMVER","events":[{"introduced":"9.0.0"},{"fixed":"9.0.1"}]}],"versions":["9.0.0"]}],"products":[{"vendor":"matrix","product":"matrix-appservice-bridge"},{"vendor":"matrix-org","product":"matrix-appservice-bridge"}],"references":[{"url":"https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-vc7j-h8xg-fv5x","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/4c6723a5e7beda65cdf1ae5dbb882e8beaac8552","tags":["x_refsource_MISC","x_transferred","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2023-38691","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-vc7j-h8xg-fv5x"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/38xxx/CVE-2023-38691.json","tags":["advisory"]},{"url":"https://github.com/matrix-org/matrix-appservice-bridge","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2023-38691","title":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","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.","status":"published","published":"2023-08-04T16:34:54.312Z","modified":"2024-10-07T13:01:29.642Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T14:35:29.772612Z"}],"euvd":[{"id":"EUVD-2023-2361","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.","status":"published","published":"2023-08-04T16:34:54Z","modified":"2024-10-07T13:01:29Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium"}],"updated_at":"2026-11-03T00:27:49.014643Z"}],"ghsa":[{"id":"GHSA-vc7j-h8xg-fv5x","title":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","description":"### 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","status":"published","published":"2023-08-04T17:26:32Z","modified":"2023-11-07T05:05:25Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T14:37:15.931647Z"}],"nvd":[{"id":"CVE-2023-38691","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.","status":"published","published":"2023-08-04T17:15:11.063Z","modified":"2026-06-17T06:10:57.813Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T14:08:20.798312Z"}],"osv":[{"id":"CVE-2023-38691","title":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","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.","status":"published","published":"2023-08-04T16:34:54.312Z","modified":"2026-10-28T02:30:38.480332484Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T15:44:32.922049Z"},{"id":"GHSA-vc7j-h8xg-fv5x","title":"matrix-appservice-bridge doesn't verify the sub parameter of an openId token exhange, allowing unauthorized access to provisioning APIs","description":"### 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","status":"published","published":"2023-08-04T17:26:32Z","modified":"2026-09-10T03:49:57.718797886Z","cvss":[{"version":"3.1","score":5,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N","level":"medium"}],"cwes":["CWE-287"],"updated_at":"2026-11-02T15:46:56.981655Z"}]}}