Description

A compact Beacon Object File has been created to siphon authentication cookies from Microsoft Teams without crashing or altering the running app, offering a stealthy alternative to blunt process termination. Building on research that revealed where Teams stores tokens, the tool adapts a live-browser cookie-extraction technique so attackers can impersonate users and access chats, files, and Office 365 APIs. The authors traced the weakness to Teams’ embedded Chromium-based webview (msedgewebview2.exe), which persists cookies in a SQLite store much like a browser does, but protects them using the simpler, user-bound Windows Data Protection API. Modern Chromium browsers instead rely on a COM-based service (IElevator) running as SYSTEM to guard encryption keys, raising the bar for remote decryption — a protection Teams’ DPAPI approach does not match. To avoid noisy tactics such as killing MS-Teams.exe, the new BOF injects into the Teams process (or any same-privilege process), locates child webview processes that hold open handles to the Cookies file, duplicates those handles, and decrypts entries on-the-fly using the user’s DPAPI master key. That method mirrors the Cookie-Monster approach but repurposes it for messaging apps, which increases stealth while also producing detectable handle-and-injection patterns. Because the resulting tokens permit API-driven access to conversations and Graph resources, the release — available as a Beacon payload on GitHub — should prompt defenders to harden endpoints: monitor for unusual handle operations and DPAPI access, enforce least privilege, and add behavioral rules to catch process injection into webview hosts.