GHSA-35g4-qx3c-vjhx Automatic room upgrade handling can be used maliciously to bridge a room non-consentually

• npm matrix-appservice-bridge: < 2.6.1 → fixed in 2.6.1

Impact 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 mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware. Patches Versions 2.6.1 and greater are patched. Workarounds Disabling the automatic room upgrade handling can be done by removing the `roomUpgradeOpts` key from the `Bridge` class options. References The issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330 For more information] If you have any questions or comments about this advisory, email us at [email protected].