[New Rule] AWS Lambda Execution Role Credentials Used Outside Lambda

[bryans3c]

Pull Request

Issue link(s):

• https://github.com/elastic/ia-trade-team/issues/920

Summary - What I changed

Add detection of a single AWS Lambda execution-role credential (a temporary assumed-role access key) that is used both from inside the Lambda execution environment and from outside it within the same window. When a function runs, its temporary credentials are presented with the Lambda runtime user agent (containing "exec-env/AWS_Lambda") or with a request invoked by "lambda.amazonaws.com". An adversary who exfiltrates those credentials, typically through a server-side request forgery or remote code execution flaw in the function, can replay them from their own host, where the same
access key appears without the Lambda runtime markers and from an unrelated source. Observing the same temporary key
both inside and outside the runtime is a strong indicator of stolen Lambda credentials being abused.

How To Test

Query & data can be assessed in TRADE stack and other telemetry stacks.

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?

[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.

[Copilot]

Pull request overview

Adds a new AWS CloudTrail ES|QL detection rule intended to identify potential theft and replay of AWS Lambda execution-role temporary credentials by correlating usage of the same assumed-role access key both inside the Lambda runtime and from an external/non-Lambda context.

Changes:

• Introduces a new ES|QL aggregation rule that groups CloudTrail activity by temporary access key id and flags keys used both with Lambda runtime markers and without them in the same window.
• Adds an investigation guide with triage, false positive, and remediation guidance specific to Lambda credential replay scenarios.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 3 comments.

[terrancedejesus]

Couple of considerations. Logic and threat signal! Nice rule!

[imays11]

The only time I see this invoked_by value is when aws.cloudtrail.user_identity.type == AWSService, how are you comparing these AssumedRole lambda calls to the original service Lambda calls?