{"id":"CVE-2021-32659","aliases":["EUVD-2021-1248","GHSA-35g4-qx3c-vjhx"],"status":"published","title":"Automatic room upgrade handling can be used maliciously to bridge a room non-consentually","description":"Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, if a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.","severity":{"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":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00936,"percentile":0.61111,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-306"],"published":"2021-06-16T18:45:11Z","modified":"2026-10-20T10:54:43Z","fixes":[{"ecosystem":"npm","package":"matrix-appservice-bridge","fixed_in":["2.6.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.6.1"}]}]},{"source":"osv","ecosystem":"npm","package":"matrix-appservice-bridge","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.6.1"}]}]}],"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-35g4-qx3c-vjhx","tags":["x_refsource_CONFIRM","x_transferred","Mitigation","Third Party Advisory","advisory","web"]},{"url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/b69e745584a34fcfd858df33e4631e420da07b9f","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/matrix-org/matrix-appservice-bridge/releases/tag/2.6.1","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-32659","tags":["advisory"]},{"url":"https://github.com/matrix-org/matrix-appservice-bridge/pull/330","tags":["web"]},{"url":"https://github.com/advisories/GHSA-35g4-qx3c-vjhx"}],"sources":{"cve":[{"id":"CVE-2021-32659","title":"Automatic room upgrade handling can be used maliciously to bridge a room non-consentually","description":"Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, if a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.","status":"published","published":"2021-06-16T18:45:11Z","modified":"2024-08-03T23:25:31.074Z","cvss":[{"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":"cna"}],"cwes":["CWE-306"],"updated_at":"2026-11-02T14:33:07.014772Z"}],"euvd":[{"id":"EUVD-2021-1248","description":"Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, if a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.","status":"published","published":"2021-06-16T18:45:11Z","modified":"2024-08-03T23:25:31Z","cvss":[{"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"}],"updated_at":"2026-11-03T03:24:36.41075Z"}],"ghsa":[{"id":"GHSA-35g4-qx3c-vjhx","title":"Automatic room upgrade handling can be used maliciously to bridge a room non-consentually ","description":"### Impact\n\nIf a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware.\n\n\n### Patches\n\nVersions 2.6.1 and greater are patched.\n\n### Workarounds\n\nDisabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options. \n\n### References\n\nThe issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330\n\n### For more information]\n\nIf you have any questions or comments about this advisory, email us at security@matrix.org.","status":"published","published":"2021-06-21T17:09:22Z","modified":"2023-02-01T05:06:08Z","cvss":[{"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"}],"cwes":["CWE-306"],"updated_at":"2026-11-02T14:36:37.441118Z"}],"nvd":[{"id":"CVE-2021-32659","description":"Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, if a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.","status":"published","published":"2021-06-16T19:15:38.83Z","modified":"2026-06-17T03:53:22.01Z","cvss":[{"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":"secondary"},{"version":"3.1","score":4.9,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"primary"},{"version":"2.0","score":3.5,"vector":"AV:N/AC:M/Au:S/C:N/I:P/A:N","level":"low","assessor":"primary"}],"cwes":["CWE-306"],"updated_at":"2026-11-02T14:06:54.892562Z"}],"osv":[{"id":"CVE-2021-32659","description":"Matrix-appservice-bridge is the bridging service for the Matrix communication program's application services. In versions 2.6.0 and earlier, if a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any malicious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Versions 2.6.1 and greater are patched. As a workaround, disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options.","status":"published","published":"2021-06-16T19:15:38.83Z","modified":"2026-10-20T10:54:43.349026922Z","cvss":[{"version":"3.1","score":4.9,"vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T15:44:19.793849Z"},{"id":"GHSA-35g4-qx3c-vjhx","title":"Automatic room upgrade handling can be used maliciously to bridge a room non-consentually ","description":"### Impact\n\nIf a bridge has room upgrade handling turned on in the configuration (the `roomUpgradeOpts` key when instantiating a new `Bridge` instance.), any `m.room.tombstone` event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room `m.room.create` event is not checked to verify if the `predecessor` field contains the previous room. This means that any mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware.\n\n\n### Patches\n\nVersions 2.6.1 and greater are patched.\n\n### Workarounds\n\nDisabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options. \n\n### References\n\nThe issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330\n\n### For more information]\n\nIf you have any questions or comments about this advisory, email us at security@matrix.org.","status":"published","published":"2021-06-21T17:09:22Z","modified":"2026-07-08T06:29:05.568084068Z","cvss":[{"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"}],"cwes":["CWE-306"],"updated_at":"2026-11-02T15:46:35.050232Z"}]}}