[New Rule] Web Server Unusual Spike in Error Response Codes

[Aegrah]

Summary

This rule detects unusual spikes in error response codes (500, 502, 503, 504) from web servers, which may indicate reconnaissance activities such as vulnerability scanning or fuzzing attempts by adversaries. These activities often generate a high volume of error responses as they probe for weaknesses in web applications. Error response codes may potentially indicate server-side issues that could be exploited.

Telemetry

[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

• ❌ Web Server Unusual Spike in Error Response Codes (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Web Server Unusual Spike in Error Response Codes (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Web Server Unusual Spike in Error Response Codes (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Web Server Unusual Spike in Error Response Codes (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[tradebot-elastic]

⛔️ Test failed

Results

• ❌ Web Server Unusual Spike in Error Response Codes (esql)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[terrancedejesus]

My concern here is that if there is an outage out of the customer's control and it is a popular site, then this may get noisy. Maybe BBR first? Would be interesting to see an adjacent 404 from single address rule (fuzzing).