Telegram Rapid Meeting Invite Fan-Out Excluding Known Bots (GhostCall)

Duo Tech@duotech

•updated Jul 24, 2026•1•0•6

Detects rapid outbound meeting-invite fan-out from a Telegram account to numerous contacts (RecipientCount >= 10), excluding accounts flagged as known legitimate bulk-messaging/bot accounts, consistent with BlueNoroff's GhostCall self-propagation pipeline where compromised trusted-contact accounts distribute fake meeting invites. This rule captures only the fan-out behavior; for full GhostCall self-propagation confirmation it should ideally be paired with a companion rule detecting Telegram session reuse on a new device/IP (same UserId, within approximately 15 minutes), since that temporal join between session hijack and invite fan-out cannot be expressed as a single Sigma query.