Suspicious Cisco Duo Successful MFA Authentication Through Bypass Code (via duo)

title: Suspicious Cisco Duo Successful MFA Authentication Through Bypass Code (via duo)
id: 59b8e302-fefa-5c51-87c0-e779e1d631ba
status: stable
description: This rule detects when a successful MFA authentication occurs due to the use of a bypass code. A bypass code is a temporary passcode created by an administrator for a specific user to access a Duo-protected application. These are generally used as "backup codes," so that enrolled users who are having problems with their mobile devices (e.g., mobile service is disrupted, the device is lost or stolen, etc.) or who temporarily can't use their enrolled devices (on a plane without mobile data services) can still access their Duo-protected systems.
references:
    - https://duo.com/docs/adminapi#logs
    - https://help.duo.com/s/article/6327?language=en_US
author: Huntrule Team
date: 2026-01-11
tags:
    - attack.credential-access
    - attack.initial-access
    - attack.stealth
    - attack.defense-evasion
    - attack.t1078
    - attack.t1556.006
logsource:
    product: cisco
    service: duo
detection:
    selection:
        event_type: authentication
        reason: bypass_user
    condition: selection
falsepositives:
    - Unknown
level: medium