Bulk mailbox-permission grants correlated with risky/device-code admin sign-in

Arnold Chan@slaz

•updated Sep 23, 2026•1•0•2

Detects an administrator account rapidly granting mailbox permissions (Add-MailboxPermission, Add-RecipientPermission, Set-MailboxFolderPermission) to a large number of objects within a short timeframe (15 minutes). The rule correlates this activity with a prior 'risky' sign-in or a sign-in using device-code flow, indicative of potential EvilToken or similar adversary-in-the-middle proxy-based session hijacking.