[New Rule] Manual Mount Discovery via /etc/exports

[Aegrah]

Summary

This rule detects manual mount discovery via the /etc/exports file on Linux systems. The /etc/exports file is used by NFS (Network File System) to define which directories are shared with remote hosts. Attackers may access this file to gather information about shared directories and potential targets for further exploitation.

Telemetry

In test stacks only TPs, in telemetry last 90d 0 hits.

BBR consideration

Given the fact that this activity is not very common, and having writeable shares or misconfigured shares with e.g. NO_ROOT_SQUASH enabled is a common attack vector, my opinion is this deserves to be a DR rather than BBR.

[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

• ❌ Manual Mount Discovery via /etc/exports (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Manual Mount Discovery via /etc/exports or /etc/fstab (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[terrancedejesus]

Thoughts on adding some other file inspection commands --> awk, head, vi, etc.

I agree that this should be fine as a detection rule. My only thought would be random backend monitoring jobs done by admins, but that should just be a manual exception.

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Manual Mount Discovery via /etc/exports or /etc/fstab (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta