Description

TeamsPhisher, a newly released tool developed by a member of the US Navy's red team, exploits an unsolved security vulnerability in Microsoft Teams, allowing individuals outside of the targeted organization to bypass restrictions on inbound files from external tenants. The software exploits a previously identified vulnerability by Max Corbridge and Tom Ellson, security specialists from the UK-based company Jumpsec, demonstrating how an attacker could easily bypass Microsoft Teams' file-sending restrictions and transmit malware via an external account. Due to the application's client-side safety features, which may be managed to treat an external user as an internal one by changing the ID in a message's POST request, this attack is feasible. The attack concept from Jumpsec researchers is combined with Andrea Santese's techniques, and Bastian Kanbach's TeamsEnum tool's authentication to develop TeamsPhisher, a Python-based application that provides a full automated attack solution. Users may utilize TeamsPhisher to upload an attachment to their SharePoint by supplying an attachment, a message, and a list of target Teams users. First, the software validates the target user's existence and ability to receive external communications, which is required for the attack. Then it starts a new thread with the target and sends them a message with a SharePoint attachment link that is accessible on the sender's Teams interface and may be interacted with manually if needed. It should be noted that TeamsPhisher requires users to have a Microsoft Business account with a valid Teams and SharePoint license, which is typical in many large corporations.