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[New] Command Line Obfuscation via Whitespace Padding #4860

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@Samirbous Samirbous self-assigned this Jun 30, 2025
@Samirbous Samirbous added Rule: New Proposal for new rule OS: Windows windows related rules labels Jun 30, 2025
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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.

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Starting the rule tests ...

@Samirbous Samirbous requested a review from w0rk3r June 30, 2025 10:07
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Starting the rule tests ...

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Starting the rule tests ...

…l to defense_evasion_whitespace_padding_command_line.toml
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Starting the rule tests ...

@Samirbous Samirbous changed the title [New] Command Line Obfuscation via Whitespace Padding" [New] Command Line Obfuscation via Whitespace Padding Jun 30, 2025
severity = "medium"
tags = [
"Domain: Endpoint",
"OS: Windows",
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Suggested change
"OS: Windows",
"OS: Windows",
"OS: macOS",
"OS: Linux",

@@ -0,0 +1,128 @@
[metadata]
creation_date = "2025/06/30"
integration = ["endpoint", "system", "windows", "auditd_manager", "m365_defender", "crowdstrike"]
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s1 maybe? cc @w0rk3r


query = '''
FROM logs-* metadata _id, _version, _index
| where event.category == "process" and event.type == "start"
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Suggested change
| where event.category == "process" and event.type == "start"
| where event.category == "process" and (
(host.os.type == "windows" and event.type == "start") or
(host.os.type == "macos" and event.type == "start" and event.action == "exec") or
(host.os.type == "linux" and event.type == "start" and event.action in ("exec", "exec_event", "start", "executed", "process_started")
)

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Might help reduce FPs from the start by excluding forks

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@Aegrah Aegrah Jun 30, 2025

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Not sure if we need to use match here instead because of the bug with using in.

type = "esql"

query = '''
FROM logs-* metadata _id, _version, _index
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We may want to limit the indexes here, logs-* would probably be expensive as it will search for all integrations

@zez3
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zez3 commented Jul 1, 2025

This supersedes the old deprecated rule #2315

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5 participants