Detection rules › Sigma
Potential MFA Bypass Using Legacy Client Authentication
Detects successful authentication from potential clients using legacy authentication via user agent strings. This could be a sign of MFA bypass using a password spray attack.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Initial Access | T1078.004 Valid Accounts: Cloud Accounts |
| Persistence | T1078.004 Valid Accounts: Cloud Accounts |
| Privilege Escalation | T1078.004 Valid Accounts: Cloud Accounts |
| Stealth | T1078.004 Valid Accounts: Cloud Accounts |
| Credential Access | T1110 Brute Force |
Rule body yaml
title: Potential MFA Bypass Using Legacy Client Authentication
id: 53bb4f7f-48a8-4475-ac30-5a82ddfdf6fc
status: test
description: Detects successful authentication from potential clients using legacy authentication via user agent strings. This could be a sign of MFA bypass using a password spray attack.
references:
- https://web.archive.org/web/20230217071802/https://blooteem.com/march-2022
- https://www.microsoft.com/en-us/security/blog/2021/10/26/protect-your-business-from-password-sprays-with-microsoft-dart-recommendations/
author: Harjot Singh, '@cyb3rjy0t'
date: 2023-03-20
tags:
- attack.privilege-escalation
- attack.persistence
- attack.initial-access
- attack.credential-access
- attack.stealth
- attack.t1078.004
- attack.t1110
logsource:
product: azure
service: signinlogs
detection:
selection:
Status: 'Success'
userAgent|contains:
- 'BAV2ROPC'
- 'CBAinPROD'
- 'CBAinTAR'
condition: selection
falsepositives:
- Known Legacy Accounts
level: high
Stages and Predicates
Stage 0: condition
selectionStage 1: selection
selection:
Status: 'Success'
userAgent|contains:
- 'BAV2ROPC'
- 'CBAinPROD'
- 'CBAinTAR'
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.