ParaChat Server 4.0 does not log users off if the browser's back button is used, which allows remote attackers to cause a denial of service by repeatedly logging into a chat room, hitting the back button, then logging into the same chat room as a different user, which fills the chat room with invalid users.

Directory traversal vulnerability in ParaChat Server 5.5 allows remote attackers to read arbitrary files via a ..%5C (hex-encoded dot dot) in the URL.