Matrix IRC Bridge allows IRC command injection to own puppeted user

Vulnerability

Overview The matrix-appservice-irc bridge, a Node.js IRC bridge for Matrix, contains a vulnerability in versions prior to 3.0.4 that allows arbitrary IRC command execution. The root cause is insufficient sanitization of input when setting a Matrix room topic, which is then forwarded to IRC through the TOPIC command. When a Matrix user changes a room topic containing newline characters, the bridge passes the raw string to the IRC server, effectively allowing an attacker to inject additional IRC commands on the same connection. The fix, introduced in commit 74f02c8e11f16ed1b355700092c1aa9c036a11bd, replaces newline characters (\n) with pipes (|) and strips carriage returns (\r) before sending the topic to IRC. [1][3][4]

Attack

Vector Exploitation requires the attacker to be a Matrix user who has permission to change the room topic in a bridged channel. The attacker sets a topic containing newlines followed by arbitrary IRC commands (e.g., /msg, JOIN, PRIVMSG). When the bridge processes the topic change, it forwards the unsanitized string to the IRC server via the TOPIC command, causing the injected newlines to terminate the TOPIC command and execute subsequent lines as new IRC commands. The attack is limited to the attacker's own IRC user context, meaning the attacker cannot impersonate other users or execute commands as a different IRC client. [1][4]

Impact

A successful attack allows the attacker to execute arbitrary IRC commands as their own bridged user, potentially including actions such as joining or leaving channels, sending private messages, changing nicknames, or interacting with IRC services (e.g., NickServ commands). The scope is limited to the attacker's own puppeted IRC client, so there is no privilege escalation to other users or to the bridge itself. Commands are executed with the permissions and capabilities of the attacker's IRC account. [1][4]

Mitigation

The vulnerability has been patched in matrix-appservice-irc version 3.0.4. All users running a version prior to 3.0.4 should update immediately to the latest release. No workarounds are documented. The attack surface is limited to topic changes, but bridge operators should ensure timely patching to prevent abuse. [1][4]