[Rule Tuning] Microsoft Entra ID MFA TOTP Brute Force Attempts

[terrancedejesus]

Pull Request

Issue link(s):

• https://github.com/elastic/sdh-protections/issues/599

Summary - What I changed

Tunes the Microsoft Entra ID MFA TOTP Brute Force Attempts rule for the following:

• Update name to Microsoft Entra ID MFA TOTP Brute Force Attempts
• Updated description as query logic has been adjusted
• Investigation guide updates to stay consistent with investigation guide formats and be more agnostic
• Updated tags to stay consistent with naming
• Updated rule query
  • Only filter on azure.signinlogs.properties.mfa_detail.auth_method == "OATH verification code" and not MFA. This infers MFA was used.
  • Added azure.signinlogs.properties.user_type == "Member" to ensure it only flags on user accounts.
  • Focus on failure attempts reported for login or error code 500121 which reflects STS500121
  • Added several VALUES() statements to retain field values for alert
  • IMPORTANT - Added Esql.azure_signinlogs_properties.session_id_count_distinct = COUNT_DISTINCT(azure.signinlogs.properties.session_id) and then aggregated by the count. As reported by Oasis security, not only are multiple TOTP codes used, but multiple sessions which were the original brute force method. This should be higher fidelity as multiple sessions for multiple TOTP are not common unless pentesting or actual brute forcing.

NOTE - < 100 alerts in the last 6 months for this rule, no FP adjustments needed.

How To Test

Query can be used in TRADE stack, use Esql.azure_signinlogs_properties.session_id_count_distinct >= 8.

Checklist

• Added a label for the type of pr: bug, enhancement, schema, maintenance, Rule: New, Rule: Deprecation, Rule: Tuning, Hunt: New, or Hunt: Tuning so guidelines can be generated
• Added the meta:rapid-merge label if planning to merge within 24 hours
• Secret and sensitive material has been managed correctly
• Automated testing was updated or added to match the most common scenarios
• Documentation and comments were added for features that require explanation

Contributor checklist

• Have you signed the contributor license agreement?
• Have you followed the contributor guidelines?

[github-actions]

Rule: New - Guidelines

These guidelines serve as a reminder set of considerations when proposing a new rule.

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• Detailed description of the rule.
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• Link related issues or PRs.
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[Mikaayenson]

@terrancedejesus this rule hasn't changed ever since it was first created. The only thing that may have changed in May is the release (potentially integrations package). Is the issue just the data or did the integration change from May (or anything else)?

[terrancedejesus]

@Mikaayenson - The core issue reported was based on the logic and what was being reported in the environment. Mainly, SFA when CAPs are not applied during a TOTP workflow. Also the query needed adjusted to aggregate by unique session IDs as well, not just attempts. More details are in the issue but I am happy to discuss further.