AWS Lambda Function Invoked by an Unusual Principal

Description

Identifies the first time within the prior 14 days that a principal directly invokes an AWS Lambda function in an account, excluding invocations made on behalf of AWS services (normal event-source triggers). Adversaries who compromise credentials or move laterally may directly invoke functions to execute code, retrieve data returned by a function, or abuse an over-permissioned execution role. Direct, ad hoc invocation by a principal that does not normally call Lambda deviates from the usual event-driven invocation pattern and is worth reviewing. This rule relies on AWS Lambda data event logging, which is not enabled by default.

Detection logic

Its licence does not clear it for publishing here

Sunturai publishes a detection's own text where the licence it arrived under has been reviewed and permits it, and Elastic License 2.0 has not. The query as its source wrote it, its canonical form and the hash that pins this revision are in the workspace record.

Detection requirements

Platform: IaaS Office Suite SaaS
The rule states no platform. This is derived from the ATT&CK technique it maps to.
Log source category: event_index

Known benign triggers

Developers, operators, and CI/CD or automation identities legitimately invoke functions directly for testing, operations, and deployments. New automation roles or first-time operators will generate this alert. Verify the principal in `aws.cloudtrail.user_identity.arn`, the function, and the source before treating it as malicious, and exclude known operational identities after validation.

References

Links the source published beside this detection. Reference is the link the source wrote, unmodified. Class is decided by this catalogue from the host and path, not stated by the source. Cited by counts published detections citing the same resource, including this one, and the sources beneath it count the repositories this catalogue ingests, which is not the same as independent research.
Reference	Class	Cited by
docs.aws.amazon.com/lambda/latest/api/API_Invoke.html	Product documentation	2
docs.aws.amazon.com/lambda/latest/dg/logging-using-cloudtrail.html	Product documentation	5

Detection rules

AWS Lambda Function Invoked by an Unusual Principal

Description

Detection logic

Detection requirements

Known benign triggers

MITRE ATT&CK mappings

References

From the source

Licence

Authorship

Detection rules