Improper Privilege Management
matrix-appservice-irc is an open source Node.js IRC bridge for Matrix. In matrix-appservice-irc prior to 0.35.0 an 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.
CWE-269 - Improper Privilege Management
An effective privilege management infrastructure provides valid users with required access and privileges across heterogeneous technology environments. An application with a faulty privilege management infrastructure allows higher than authorized privileges or enables privilege escalation. This can lead to security incidents such as system infiltration, data breach, and complete system takeover.