A novel cross-site scripting (XSS) vulnerability at the ‘teams.microsoft.com’ domain could be abused to trigger a remote code execution flaw in the Microsoft Teams desktop application. It has about 115 million daily active users and is widely deployed as part of Microsoft’s Office 365 family of products. Teams is a proprietary business communication platform that provides users with workspace chat, file storage and sharing, app integration, and videoconferencing capabilities. An attacker simply needs to send a specially crafted message to any Teams user or channel to launch a successful exploit that runs silently in the background, without the user noticing anything.
Remote Code Execution has been achieved in desktop applications across all supported platforms (Windows, macOS, Linux). Code execution gives attackers full access to victim devices and company internal networks via those devices. An attacker could abuse the XSS flaw to obtain SSO authorization tokens for Teams or other Microsoft services, or to access confidential conversations and files from the communications service. Moreover, the vulnerability is wormable, allowing a successful attacker to automatically send the exploit payload to other users/channels, also without interaction. The successful exploitation of the bug could potentially give access to private keys and personal data outside Teams, possibly leaking internal network information and allowing adversaries to set up for phishing attacks. Remote code execution can be achieved only if the XSS in teams.microsoft.com (in user ‘mentions’ functionality) is chained with the novel cross-platform exploit for the Teams desktop clients.
The company has already addressed the vulnerability. Vulnerabilities in Microsoft Teams are fixed via automatic updates.