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[Rule Tuning] Linux DR Tuning - 4 #5484

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@Aegrah
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@Aegrah Aegrah commented Dec 17, 2025

Summary

Half of Linux Defense Evasion rules

@Aegrah Aegrah self-assigned this Dec 17, 2025
@Aegrah Aegrah added OS: Linux Rule: Tuning tweaking or tuning an existing rule Team: TRADE labels Dec 17, 2025
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github-actions bot commented Dec 17, 2025

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.

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tradebot-elastic commented Dec 17, 2025 •
edited
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⛔️ Test failed

Results
  • ❌ Potential Hex Payload Execution via Common Utility (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Hex Payload Execution via Command-Line (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ High Number of Egress Network Connections from Unusual Executable (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Defense Evasion via Doas (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Clear Kernel Ring Buffer (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Syslog Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Directory Creation in /bin directory (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ SSH Authorized Keys File Deletion (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Hidden Files and Directories via Hidden Flag (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Dynamic Linker Creation (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Auditd Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable IPTables or Firewall (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File made Immutable by Chattr (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Access Control List Modification via setfacl (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Permission Modification in Writable Directory (kuery)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Deletion via Shred (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Unusual Base64 Encoding/Decoding Activity (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Base16 or Base32 Encoding/Decoding Activity (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of SELinux (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of AppArmor (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ System Binary Moved or Copied (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta

@tradebot-elastic
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tradebot-elastic commented Dec 17, 2025 •
edited
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⛔️ Test failed

Results
  • ❌ Potential Hex Payload Execution via Common Utility (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Hex Payload Execution via Command-Line (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ High Number of Egress Network Connections from Unusual Executable (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Defense Evasion via Doas (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Clear Kernel Ring Buffer (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Syslog Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Directory Creation in /bin directory (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ SSH Authorized Keys File Deletion (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Hidden Files and Directories via Hidden Flag (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Dynamic Linker Creation (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Auditd Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable IPTables or Firewall (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File made Immutable by Chattr (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Access Control List Modification via setfacl (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Permission Modification in Writable Directory (kuery)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Deletion via Shred (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Unusual Base64 Encoding/Decoding Activity (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Base16 or Base32 Encoding/Decoding Activity (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of SELinux (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of AppArmor (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ System Binary Moved or Copied (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta

eric-forte-elastic
eric-forte-elastic reviewed Dec 18, 2025
View reviewed changes
rules/linux/command_and_control_frequent_egress_netcon_from_sus_executable.toml
process.executable like "/tmp/.mount*" or
process.executable like "/tmp/go-build*"
)
| keep
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@eric-forte-elastic eric-forte-elastic Dec 18, 2025

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For this keep I think you will need to keep the meta data too _id, _index, _version

Ref: #5441

eric-forte-elastic
eric-forte-elastic reviewed Dec 18, 2025
View reviewed changes
rules/linux/defense_evasion_base64_decoding_activity.toml
process.command_line like "*Base64.decode64*"
)
)
| keep
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@eric-forte-elastic eric-forte-elastic Dec 18, 2025

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Same for this keep I think.

Samirbous
Samirbous reviewed Dec 18, 2025
View reviewed changes
rules/linux/command_and_control_frequent_egress_netcon_from_sus_executable.toml Outdated
agent.id,
host.name
host.name,
Esql.*
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@Samirbous Samirbous Dec 18, 2025

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keep on Esql.* before being defined ?

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tradebot-elastic commented Dec 18, 2025 •
edited
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⛔️ Test failed

Results
  • ❌ Potential Hex Payload Execution via Common Utility (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Hex Payload Execution via Command-Line (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ High Number of Egress Network Connections from Unusual Executable (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Defense Evasion via Doas (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Clear Kernel Ring Buffer (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Syslog Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Directory Creation in /bin directory (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ SSH Authorized Keys File Deletion (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Hidden Files and Directories via Hidden Flag (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Dynamic Linker Creation (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Auditd Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable IPTables or Firewall (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File made Immutable by Chattr (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Access Control List Modification via setfacl (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Permission Modification in Writable Directory (kuery)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Deletion via Shred (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Unusual Base64 Encoding/Decoding Activity (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Base16 or Base32 Encoding/Decoding Activity (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of SELinux (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of AppArmor (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ System Binary Moved or Copied (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta

@tradebot-elastic
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tradebot-elastic commented Dec 18, 2025 •
edited
Loading

⛔️ Test failed

Results
  • ❌ Potential Hex Payload Execution via Common Utility (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Hex Payload Execution via Command-Line (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ High Number of Egress Network Connections from Unusual Executable (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Defense Evasion via Doas (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Clear Kernel Ring Buffer (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Syslog Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Directory Creation in /bin directory (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ SSH Authorized Keys File Deletion (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Hidden Files and Directories via Hidden Flag (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Dynamic Linker Creation (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable Auditd Service (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Attempt to Disable IPTables or Firewall (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File made Immutable by Chattr (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Access Control List Modification via setfacl (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Permission Modification in Writable Directory (kuery)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ File Deletion via Shred (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Unusual Base64 Encoding/Decoding Activity (esql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Base16 or Base32 Encoding/Decoding Activity (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of SELinux (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ Potential Disabling of AppArmor (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta
  • ❌ System Binary Moved or Copied (eql)
    • coverage_issue: no_rta
    • stack_validation_failed: no_rta

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@Samirbous Samirbous Samirbous left review comments

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backport: auto Domain: Endpoint OS: Linux Rule: Tuning tweaking or tuning an existing rule Team: TRADE

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