node-irc is a socket wrapper for the IRC protocol that extends Node.js' EventEmitter. The vulnerability allows an attacker to manipulate a Matrix user into executing IRC commands by having them reply to a maliciously crafted message. Incorrect handling of a CR character allowed for making part of the message be sent to the IRC server verbatim rather than as a message to the channel.
The vulnerability has been patched in node-irc version 1.2.1.

References

• GHSA-52rh-5rpj-c3w6
• https://matrix.org/blog/2022/05/04/0-34-0-security-release-for-matrix-appservice-irc-high-severity
• matrix-org/node-irc@2976c85
• matrix-org/node-irc@e3eb9c1