:: Deepquest ::

This report describes a vulnerability chain that enables a malicious user to compromise another user over Zoom chat. User interaction is not required for a successful attack. The only ability an attacker needs is to be able to send messages to the victim over Zoom chat over XMPP protocol. Initial vulnerability (labeled XMPP Stanza Smuggling) abuses parsing inconsistencies between XML parsers on Zoom’s client and server in order to be able to “smuggle” arbitrary XMPP stanzas to the victim client. From there, by sending a specially crafted control stanza, the attacker can force the victim client to connect to a malicious server, thus turning this primitive into a man-in-the-middle attack. Finally, by intercepting/modifying client update requests/responses, the victim client downloads and executes a malicious update, resulting in arbitrary code execution. A client downgrade attack is utilized to bypass signature check on the update installer. This attack has been demonstrated against the latest (5.9.3) client running on Windows 64-bit, however some or all parts of the chain are likely applicable to other platforms.