AWS Lambda Function Policy Updated to Allow Cross-Account Invocation

Last updated 6 days ago on 2026-06-18

Created 6 days ago on 2026-06-18

About

Identifies a change to an AWS Lambda function resource policy that grants invoke permissions to an AWS account principal. Using AddPermission, an adversary can authorize a principal in another account to call a function, creating a cross-account backdoor for execution or for relaying data to attacker-controlled infrastructure without modifying the function's code. This rule excludes public grants (principal set to "*"), which are covered by a separate rule, and grants to AWS service principals, which are common for legitimate event triggers.

Tags

Domain: CloudData Source: AWSData Source: Amazon Web ServicesData Source: AWS LambdaUse Case: Threat DetectionTactic: PersistenceTactic: Defense EvasionLanguage: eql

Severity

high

Risk Score

MITRE ATT&CK™

Persistence (TA0003)(external, opens in a new tab or window)

↳ Event Triggered Execution (T1546)(external, opens in a new tab or window)

Defense Evasion (TA0005)(external, opens in a new tab or window)

↳ Modify Cloud Compute Infrastructure (T1578)(external, opens in a new tab or window)

False Positive Examples

Cross-account invoke permissions are used for legitimate multi-account architectures and partner integrations. Verify the granted account in `aws.cloudtrail.request_parameters`, the function, and the `principal` value in `aws.cloudtrail.request_parameters` against approved cross-account access. Known partner or internal account ids can be excluded after validation. This rule cannot distinguish a grant to the function's own account from an external account, so same-account resource-policy grants (uncommon, since same-account invocation normally uses IAM identity-based policies) will also alert.

License

Elastic License v2(external, opens in a new tab or window)

Definition

Rule Type: Event Correlation Rule
Integration Pack: Prebuilt Security Detection Rules
Index Patterns: logs-aws.cloudtrail-*
Related Integrations: aws(external, opens in a new tab or window)
Query

✄𐘗text code block:
✄𐘗any where data_stream.dataset == "aws.cloudtrail"
    and event.provider == "lambda.amazonaws.com"
    and event.outcome == "success"
    and event.action : "AddPermission*"
    and stringContains(aws.cloudtrail.request_parameters, "lambda:InvokeFunction")
    and not stringContains(aws.cloudtrail.request_parameters, "principal=\\*")
    and not stringContains(aws.cloudtrail.request_parameters, ".amazonaws.com")

Install detection rules in Elastic Security

Detect AWS Lambda Function Policy Updated to Allow Cross-Account Invocation in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(external, opens in a new tab or window).