[New Rule] Unusual Azure VM Extension Installed; Suspicious Child Process via Azure VM CustomScript Extension

[terrancedejesus]

Pull Request

Issue link(s):

• https://github.com/elastic/ia-trade-team/issues/962

Summary - What I changed

Adds detection for extensions installed on Azure VMs that are not native (default) and have never been seen before azure.resource.name in the tenant. Extensions are post-install scripts that execute commands at higher system level privileges. These have historically been abused by adversaries post serial connection to VMs.

How To Test

Query can be used in TRADE stack and other telemetry stacks.

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.

Documentation and Context

• Detailed description of the rule.
• List any new fields required in ECS/data sources.
• Link related issues or PRs.
• Include references.

Rule Metadata Checks

• creation_date matches the date of creation PR initially merged.
• min_stack_version should support the widest stack versions.
• name and description should be descriptive and not include typos.
• query should be inclusive, not overly exclusive, considering performance for diverse environments. Non ecs fields should be added to non-ecs-schema.json if not available in an integration.
• min_stack_comments and min_stack_version should be included if the rule is only compatible starting from a specific stack version.
• index pattern should be neither too specific nor too vague, ensuring it accurately matches the relevant data stream (e.g., use logs-endpoint.process-* for process data).
• integration should align with the index. If the integration is newly introduced, ensure the manifest, schemas, and new_rule.yaml template are updated.
• setup should include the necessary steps to configure the integration.
• note should include any additional information (e.g. Triage and analysis investigation guides, timeline templates).
• tags should be relevant to the threat and align/added to the EXPECTED_RULE_TAGS in the definitions.py file.
• threat, techniques, and subtechniques should map to ATT&CK always if possible.

New BBR Rules

• building_block_type should be included if the rule is a building block and the rule should be located in the rules_building_block folder.
• bypass_bbr_timing should be included if adding custom lookback timing to the rule.

Testing and Validation

• Provide evidence of testing and detecting the expected threat.
• Check for existence of coverage to prevent duplication.

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[Copilot]

Pull request overview

This PR adds two new detection rules focused on Azure VM extension abuse: one control-plane rule that surfaces first-seen VM extension instance names per host from Azure Activity Logs, and one endpoint rule that detects suspicious process execution associated with the Azure CustomScript extension handler on Windows.

Changes:

• Adds an ES|QL rule to alert on first-seen (VM, extension instance name) pairs in logs-azure.activitylogs-*.
• Adds an EQL rule to detect suspicious Windows child process execution tied to CustomScriptHandler.exe.
• Includes investigation guides and ATT&CK mappings for both rules.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 10 comments.

File	Description
rules/windows/execution_azure_customscript_extension_suspicious_descendant.toml	New Windows endpoint EQL rule for suspicious process execution associated with Azure CustomScript extension activity.
rules/integrations/azure/execution_azure_vm_extension_unusual_for_host.toml	New Azure Activity Logs ES

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[bryans3c]

Only some nits. LGTM!

[bryans3c]

Just a comment: an attacker who deploys and then modifies their extension only generates one alert at deploy time. Will this be caught in a different rule?

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Suspicious Child Process via Azure VM CustomScript Extension (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Unusual Azure VM Extension Detected (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta