Quassel IRC is "a modern, cross-platform, distributed IRC client."
A vulnerability in the CTCP handling allows an attacker to trick Quassel IRC into sending arbitrary commands to the IRC server.
This can be used by an attacker for example to gain operator privileges on a channel.
A CTCP ping where the value contains a CTCP quoted newline ('\020' + 'n') will
let the Quassel core reply with a message containing an unquoted newline
('\n'). The IRC server interprets this as a command separator.
This has been fixed in version 0.3.0.3, released Oct 27 2008.