Identifies an AWS Lambda function invoked by a principal whose AWS account differs from the account that owns the function (a cross-account invocation). The caller's account is parsed from the invoking principal's ARN and compared to the function account. Adversaries who have been granted invoke permission on a function from an external account, or who operate from a separate attacker-controlled account, can use cross-account invocation to execute functions or retrieve the data they return. This is the data-plane counterpart to detecting the cross-account grant itself, and relies on AWS Lambda data event logging, which is not enabled by default.

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Identifies an AWS Lambda function invoked directly by a principal from a source network (ASN) not seen for that principal in the prior 10 days, excluding common cloud provider networks. Direct invocation from an unfamiliar external network can indicate use of stolen execution-role or user credentials from attacker-controlled infrastructure to execute functions or retrieve the data they return. This rule relies on AWS Lambda data event logging, which is not enabled by default.

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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.

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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.

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Identifies the creation or update of an AWS Lambda function URL configured with an authentication type of NONE, which exposes the function to unauthenticated invocation directly from the public internet. Adversaries can use a public function URL to establish a durable, internet-reachable entry point for command and control, data egress, or on-demand execution of attacker-controlled code, bypassing the need for valid AWS credentials to invoke the function. Function URLs with public access should be rare and deliberate, so this configuration warrants review.

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Identifies the modification of an AWS Lambda layer permission policy to grant another AWS account, an AWS Organization, or the public the ability to use a layer version. Lambda layers package code and dependencies that are loaded into the execution environment of any function that references them. Sharing a layer with an external account or with everyone can leak proprietary code or secrets bundled in the layer, and can serve as a supply-chain mechanism whereby downstream functions load attacker-influenced code. Layer sharing should be infrequent and deliberate, so newly granted external or public access warrants review.

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Identifies the deletion of an AWS Lambda function. Deleting a function removes its code, configuration, versions, and aliases. Adversaries may delete functions to disrupt business operations and automated workflows, to destroy attacker-deployed backdoors and remove evidence after achieving their objective, or to inhibit incident response. Because function deletion is destructive and often irreversible without redeployment, deletions performed by unexpected principals or outside change windows should be reviewed.

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Identifies the creation of an AWS Lambda event source mapping, which connects an event source such as an Amazon SQS queue, an Amazon Kinesis or DynamoDB stream, an Amazon MSK or self-managed Apache Kafka topic, or an Amazon MQ broker to a Lambda function so the function is automatically invoked when new records arrive. Adversaries with "lambda:CreateEventSourceMapping" permissions can abuse this to establish stealthy, event-driven persistence and execution, or to continuously siphon records from a stream or queue into attacker-controlled function code. Because the function then runs on its own whenever the source produces events, this grants durable execution without any further interactive activity by the adversary.

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Detects successful IAM API calls that create or empower IAM users and roles, attach or embed policies, or wire roles to instance profiles when the caller is an assumed role session associated with AWS Lambda. Serverless execution roles are often over-permissioned; an adversary who can run or compromise function code can abuse these APIs for privilege escalation and persistence—for example creating users or roles, issuing keys, attaching managed or inline policies, or preparing EC2 instance profiles for lateral movement.

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Detects when a single AWS resource is running multiple read-only, discovery API calls in a 10-second window. This behavior could indicate an actor attempting to discover the AWS infrastructure using compromised credentials or a compromised instance. Adversaries may use this information to identify potential targets for further exploitation or to gain a better understanding of the target's infrastructure.

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Identifies when an AWS Lambda function policy is updated to allow public invocation. This rule detects use of the AddPermission API where the Principal is set to "*", enabling any AWS account to invoke the function. Adversaries may abuse this configuration to establish persistence, create a covert execution path, or operate a function as an unauthenticated backdoor. Public invocation is rarely required outside very specific workloads and should be considered high-risk when performed unexpectedly.

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Identifies when a Lambda layer is added to an existing AWS Lambda function. Lambda layers allow shared code, dependencies, or runtime modifications to be injected into a function’s execution environment. Adversaries with the ability to update function configurations may add a malicious layer to establish persistence, run unauthorized code, or intercept data handled by the function. This activity should be reviewed to ensure the modification is expected and authorized.

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