node.js - Access denied on aws lambda function when getObject from S3 bucket

Question

I'm using the default code for a lambda function:

console.log('Loading function');

var aws = require('aws-sdk');
var s3 = new aws.S3({ apiVersion: '2006-03-01' });

exports.handler = function(event, context) {
    //console.log('Received event:', JSON.stringify(event, null, 2));

    // Get the object from the event and show its content type
    var bucket = event.Records[0].s3.bucket.name;
    var key = decodeURIComponent(event.Records[0].s3.object.key.replace(/+/g, ' '));
    var params = {
        Bucket: bucket,
        Key: key
    };

    s3.getObject(params, function(err, data) {
        if (err) {
            console.log(err);
            var message = "Error getting object " + key + " from bucket " + bucket +
                ". Make sure they exist and your bucket is in the same region as this function.";
            console.log(message);
            context.fail(message);
        } else {
            console.log('CONTENT TYPE:', data.ContentType);
            context.succeed(data.ContentType);
        }
    });
};

However i get an access denied error:

2016-02-24T14:21:21.503Z    kvyo1midvc2r69gm    Loading function 
START RequestId: baf9049b-db01-11e5-bc34-791df91353a9 Version: $LATEST 
2016-02-24T14:21:22.500Z    baf9049b-db01-11e5-bc34-791df91353a9    { [AccessDenied: Access Denied] message: 'Access Denied', code: 'AccessDenied', region: null, time: Wed Feb 24 2016 14:21:22 GMT+0000 (UTC), requestId: '215CD9BB4094E209', extendedRequestId: '0kDBEyMiJYbMApEqJuAtKct2SKLI7Z7tCBVyW6QJsYwMHROvtCEDynbGSsBdqbwFcX+YrSlGnsg=', statusCode: 403, retryable: false, retryDelay: 30 } 
2016-02-24T14:21:22.539Z    baf9049b-db01-11e5-bc34-791df91353a9    Error getting object {"originalFilename":"c12eaadf3d3b46d9b5ded6c078534c11","versions":[{"Size":1024,"Crop":null,"Max":false,"Rotate":0}]} from bucket xmovo.originalimages.develop. Make sure they exist and your bucket is in the same region as this function. 
2016-02-24T14:21:22.539Z    baf9049b-db01-11e5-bc34-791df91353a9
{
    "errorMessage": "Error getting object {"originalFilename":"c12eaadf3d3b46d9b5ded6c078534c11","versions":[{"Size":1024,"Crop":null,"Max":false,"Rotate":0}]} from bucket xmovo.originalimages.develop. Make sure they exist and your bucket is in the same region as this function."
}
END RequestId: baf9049b-db01-11e5-bc34-791df91353a9 
REPORT RequestId: baf9049b-db01-11e5-bc34-791df91353a9  Duration: 723.44 ms Billed Duration: 800 ms Memory Size: 128 MB Max Memory Used: 34 MB 

My lambda function and my S3 bucket are in the same region 'US Standart' and 'us-east-1' which are the same

IAM permission are ok for lambda function, allowing to GetObject Action,(it is set with the wizard that create the lambda function)

with all that check i have no clue why i still getting the Access Denied Error

Thanks in advance

Answer 1

Looking at your log output, I can see that the key variable contains the following string:

{"originalFilename":"c12eaadf3d3b46d9b5ded6c078534c11","versions":[{"Size":1024,"Crop":null,"Max":false,"Rotate":0}]}

I'm guessing you intended that variable to contain the string "c12eaadf3d3b46d9b5ded6c078534c11".

S3 will return a 403 error response if you don't have access, or if the key doesn't exist. Returning "access denied" in both cases is a security feature to prevent attackers from finding out what keys actually exist in your bucket.

I think you need to change this line:

decodeURIComponent(event.Records[0].s3.object.key.replace(/+/g, ' '));

to something like this:

decodeURIComponent(event.Records[0].s3.object.key.originalFilename.replace(/+/g, ' '));