[New Rule] Unusual Web Config File Access

[w0rk3r]

Summary

Detects unusual access to the web.config file, which contains sensitive credential information such as database
connection strings, machineKey validation/decryption keys, and SAML/OAuth token settings. Attackers can use the
information extracted to forge malicious __VIEWSTATE requests for persistent RCE on the web server or pivot to the SQL
server using exposed connection strings.

https://trade-cloud-threat-lab-dd975d.kb.us-east-1.aws.elastic.cloud/app/r/s/eDENF

[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

• ❌ Unusual Web Config File Access (kuery)
  • coverage_issue: no_rta
  • stack_validation_failed: no_rta

[terrancedejesus]

Is web.config a generalized filename or specific to Sharepoint & IIS? If not, maybe we add them in the rule name?

[w0rk3r]

It is specific to IIS/ASP.NET

[terrancedejesus]

Linking: https://github.com/elastic/ia-trade-team/issues/667

[Mikaayenson]

Suggested change

	event.category:file and event.action:open and file.name:"web.config"
	host.os.type:window and event.category:file and event.action:open and file.name:"web.config"