[Rule Tuning] Adjust process.code_signature.trusted condition

[w0rk3r]

Issues

Related to https://github.com/elastic/ia-trade-team/issues/678

Summary

I suggested using ?process.code_signature.trusted != true in Samir's PR in order to be compatible with S1 process.code_signature.trusted which is only set if true, but it turns out that as the field is optional, this would match any event that doesn't have this field and match the other conditions, causing FPs. This PR address that :awkward-look:

[github-actions]

Rule: Tuning - Guidelines

These guidelines serve as a reminder set of considerations when tuning an existing rule.

Documentation and Context

• Detailed description of the suggested changes.
• Provide example JSON data or screenshots.
• Provide evidence of reducing benign events mistakenly identified as threats (False Positives).
• Provide evidence of enhancing detection of true threats that were previously missed (False Negatives).
• Provide evidence of optimizing resource consumption and execution time of detection rules (Performance).
• Provide evidence of specific environment factors influencing customized rule tuning (Contextual Tuning).
• Provide evidence of improvements made by modifying sensitivity by changing alert triggering thresholds (Threshold Adjustments).
• Provide evidence of refining rules to better detect deviations from typical behavior (Behavioral Tuning).
• Provide evidence of improvements of adjusting rules based on time-based patterns (Temporal Tuning).
• Provide reasoning of adjusting priority or severity levels of alerts (Severity Tuning).
• Provide evidence of improving quality integrity of our data used by detection rules (Data Quality).
• Ensure the tuning includes necessary updates to the release documentation and versioning.

Rule Metadata Checks

• updated_date matches the date of tuning PR 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. Review to ensure the original intent of the rule is maintained.

Testing and Validation

• Validate that the tuned rule's performance is satisfactory and does not negatively impact the stack.
• Ensure that the tuned rule has a low false positive rate.

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Connection to Common Large Language Model Endpoints (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ System Public IP Discovery via DNS Query (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Network Activity to a Suspicious Top Level Domain (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Connection to Common Large Language Model Endpoints (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ System Public IP Discovery via DNS Query (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta
• ❌ Network Activity to a Suspicious Top Level Domain (eql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta