IRC mode parameter confusion in matrix-appservice-irc

Vulnerability Description

matrix-appservice-irc is an open source Node.js IRC bridge for Matrix. The Internet Relay Chat (IRC) protocol allows you to specify multiple modes in a single mode command. Due to a bug in the underlying matrix-org/node-irc library, affected versions of matrix-appservice-irc perform parsing of such modes incorrectly, potentially resulting in the wrong user being given permissions. Mode commands can only be executed by privileged users, so this can only be abused if an operator is tricked into running the command on behalf of an attacker. The vulnerability has been patched in matrix-appservice-irc 0.35.0. As a workaround users should refrain from entering mode commands suggested by untrusted users. Avoid using multiple modes in a single command.

References

• https://github.com/matrix-org/matrix-appservice-irc/security/advisories/GHSA-cq7q-5c67-w39w
• https://github.com/matrix-org/matrix-appservice-irc/commit/5f87dbed87b4b6dc49b7965ff152ee8535719e67
• https://matrix.org/blog/2022/09/13/security-release-of-matrix-appservice-irc-0-35-0-high-severity/