Suspicious OAuth Device Code Sign-In to Authentication Broker via Tycoon 2FA

ATT&CK techniques

Initial Access → Cred Access

Recon
Resource Dev
Initial Access
- T1078.004Cloud Accounts
Execution
Persistence
- T1078.004Cloud Accounts
Priv Esc
- T1078.004Cloud Accounts
Defense Evasion
- T1078.004Cloud Accounts
Cred Access
- T1528Steal Application Access Token
- T1539Steal Web Session Cookie
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects a successful device code authentication against the Microsoft Authentication Broker application. Tycoon 2FA operators adopted OAuth device code phishing to trick users into authorizing attacker-controlled sessions and mint long-lived tokens for non-interactive Exchange and Graph access. Device code grants to the broker app are rare in normal use and indicate token theft.

Reporting behind it

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Suspicious OAuth Device Code Sign-In to Authentication Broker via Tycoon 2FA

Pivot detection · T1078.004 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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