[New Rule] Adding Coverage for AWS S3 Unauthenticated Object Retrieval by Rare Source

[terrancedejesus]

Pull Request

Issue link(s):

• https://github.com/elastic/ia-trade-team/issues/272

Summary - What I changed

Adding detection coverage for AWS S3 Unauthenticated Object Retrieval by Rare Source.

This rule detects attempts to retrieve objects from an AWS S3 bucket by an unauthenticated source, which could indicate a misconfigured bucket policy allowing public access. Adversaries can exploit this misconfiguration by using tools or AWS CLI options like --no-sign-request to access bucket contents.

The rule triggers when an unauthenticated IP address retrieves an object, and that IP has not been seen in the last 7 days.

How To Test

• https://github.com/elastic/pwncloud/pull/10

Checklist

• Added a label for the type of pr: bug, enhancement, schema, maintenance, Rule: New, Rule: Deprecation, Rule: Tuning, Hunt: New, or Hunt: Tuning so guidelines can be generated
• Added the meta:rapid-merge label if planning to merge within 24 hours
• Secret and sensitive material has been managed correctly
• Automated testing was updated or added to match the most common scenarios
• Documentation and comments were added for features that require explanation

Contributor checklist

• Have you signed the contributor license agreement?
• Have you followed the contributor guidelines?

[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.

[Aegrah]

I reviewed three rules, and the only difference between the three seems to be the event.action, for get, list and put objects. Wouldn't it make more sense to create one rule that is called something along the lines of "AWS S3 Unauthenticated Object Activity by Rare Source", that contains event.action:(GetObject or ListObjects or PutObject)?

new terms rule type is relatively expensive, so minimizing the number of rules would make sense here I think. Rule logics:

event.dataset: "aws.cloudtrail"
    and event.provider: "s3.amazonaws.com"
    and event.action: "GetObject"
    and event.outcome: "success"
    and aws.cloudtrail.user_identity.type: ("AWSAccount" or "Unknown")
    and cloud.account.id: "anonymous"

event.dataset: "aws.cloudtrail"
    and event.provider: "s3.amazonaws.com"
    and event.action: "ListObjects"
    and event.outcome: "success"
    and aws.cloudtrail.user_identity.type: ("AWSAccount" or "Unknown")
    and cloud.account.id: "anonymous"

event.dataset: "aws.cloudtrail"
    and event.provider: "s3.amazonaws.com"
    and event.action: "PutObject"
    and event.outcome: "success"
    and aws.cloudtrail.user_identity.type: ("AWSAccount" or "Unknown")
    and cloud.account.id: "anonymous"

[terrancedejesus]

@Aegrah

I reviewed three rules, and the only difference between the three seems to be the event.action, for get, list and put objects. Wouldn't it make more sense to create one rule that is called something along the lines of "AWS S3 Unauthenticated Object Activity by Rare Source", that contains event.action:(GetObject or ListObjects or PutObject)?

This is a good point, I need to reconsider if we add 1 rule with the different API actions or keep them separated. The goal is to identify anonymous collection or discovery in general. Initially I kept them separate for tuning or exception purposes. However, They often co-exist in workflows just based on how S3 bucket/object works.

Going to put these back in draft until I do some further testing.