[New Rule] Unusual Preload Environment Variable Process Execution

[Aegrah]

Summary

This rule detects processes that are executed with environment variables that are not commonly used. This could indicate an attacker is attempting to hijack the execution flow of a process by loading malicious libraries or binaries into the process memory space.

[protectionsmachine]

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.

[terrancedejesus]

Should you aggregate the executable in here as well? If I understand correctly, the rule will trigger anytime a process is started as long as environment variables are different?

[Aegrah]

If I were to do that, we would get an alert for every time a new executable is started with an LD_PRELOAD environment variable that is new. That would mean that if you load a new LD_PRELOAD shared object, you will get tons of alerts for every executable that is ran after.

Not adding the process executable will ensure that it just flags any new entry to the LD_PRELOAD environment variables, and just alerts once.

[Aegrah]

LD_PRELOAD is also a development feature, so I don't want to cause alert fatigue