{"id":"CVE-2021-32659","aliases":["GHSA-35g4-qx3c-vjhx"],"url":"https://o3.security/vulnerability/CVE-2021-32659","summary":"Automatic room upgrade handling can be used maliciously to bridge a room non-consentually ","details":"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.","published":"2021-06-16T19:15:38.830Z","modified":"2026-07-09T12:19:58.409609Z","cvss":{"score":4.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"matrix-appservice-bridge","fixedVersion":"2.6.1"}],"fix":{"url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/b69e745584a34fcfd858df33e4631e420da07b9f","label":"matrix-org/matrix-appservice-bridge@b69e745"},"references":[{"type":"ADVISORY","url":"https://github.com/matrix-org/matrix-appservice-bridge/security/advisories/GHSA-35g4-qx3c-vjhx"},{"type":"FIX","url":"https://github.com/matrix-org/matrix-appservice-bridge/commit/b69e745584a34fcfd858df33e4631e420da07b9f"},{"type":"FIX","url":"https://github.com/matrix-org/matrix-appservice-bridge/releases/tag/2.6.1"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T12:19:58.409609Z"}}