matrix-appservice-irc is an open source Node.js IRC bridge for Matrix. Attackers can specify a specific string of characters, which would confuse the bridge into combining an attacker-owned channel and an existing channel, allowing them to grant themselves permissions in the channel. The vulnerability has been patched in matrix-appservice-irc 0.35.0. As a workaround operators may disable dynamic channel joining via `dynamicChannels.enabled` to prevent users from joining new channels, which prevents any new channels being bridged outside of what is already bridged, and what is specified in the config.