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.