[New Rule] AWS IAM User or Role Created Cloudformation Stack for First Time

[imays11]

Issue link(s):

• https://github.com/elastic/ia-trade-team/issues/346

Summary - What I changed

This rule detects the first time a principal calls AWS Cloudwatch CreateStack or CreateStackSet API. Cloudformation is used to create a single collection of cloud resources called a stack, via a defined template file. An attacker with the appropriate privileges could leverage Cloudformation to create specific resources needed to further exploit the environment. This is a new terms rule that looks for the first instance of this behavior in the last 10 days for a role or IAM user within a particular account.

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The fields chosen for new_terms is very intentional here. I needed to account for both Roles and IAM user types. The problem with Roles and new_terms is that there is a session_name attached to the role_name which is different every time a new session is created using that particular role. This means for fields like user.id or aws.cloudtrail.user_identity.arn, we can't isolate the role name itself, instead we are capturing the role name and the session name which will mean lots of false positives because every role.name+session.name combination will appear to be "new". I could utilize aws.cloudtrail.user_identity.session_context.session_issuer.arn if I were only concerned with capturing events from AssumedRoles, but since I want to capture events for long-term IAM users as well, this field won't work as it's only created when Roles are assumed. This leaves us with user.name field. The only problem here was that in an "Organization" there can be several different accounts with different cloud.account.ids all being monitored through the same Cloudtrail logs. IAM User and Role names can be duplicated across different accounts, which might create false positives if those logs are being ingested together. To correct for this I am using both user.name and cloud.account.id as the new_terms_fields value so that ideally this rule will trigger for the first time occurance of a unique role/user name + cloud.account.id combination.

Checklist

• [x] Added a label for the type of pr: bug, enhancement, schema, Rule: New, Rule: Deprecation, Rule: Tuning, Hunt: New, or Hunt: Tuning so guidelines can be generated
• [x] Secret and sensitive material has been managed correctly
• [x] Documentation and comments were added for features that require explanation

[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.