huntress.comwriteupπ‘οΈ SecurityHuntress researcher Andrew Schwartz demonstrates a novel OAuth token-theft technique: a sideloaded AppX package registered via Add-AppxPackage -Register (requiring only Developer Mode, no admin beyond that toggle) can set ContentUriRules WindowsRuntimeAccess="all" so attacker-controlled JavaScript rendered inside the Microsoft-signed WWAHost.exe process gets full WinRT access, including the legacy WebAuthenticationBroker OAuth API. Using Microsoft Office's own client ID and the oob redirect URI, the attacker triggers a genuine login.microsoftonline.com/MFA dialog with no browser chrome, captures the auth code, and exchanges it for an access token plus a long-lived refresh token carrying the full Office delegated Graph scope set (mail, files, Teams, directory, AuditLog.Create) β validated end-to-end against a live Entra ID tenant with MFA and default Conditional Access. The post frames it as a class of vulnerable signed AppX host binaries sharing the same WinRT activation layer, and provides a Sigma rule keyed on the MSAppHost/3.0 EdgeHTML user agent reaching non-Microsoft destinations, plus Sysmon/Event ID and GPO-based mitigations (restricting Developer Mode, Conditional Access, shorter refresh-token lifetimes, CAE).
WindowsOAuthMicrosoft Entra ID+4
WWAHost.exeWebAuthenticationBrokeraskWAM+8
Identity & Access, Offensive Security, Blue Team & DetectionΒ· Published and added 23 Sep 2026