S3 presigned url file upload – nodeJS + client

Question

tl;dr – OPTIONS request made from the browser to a presigned url acquired from a server (AWS S3) gets 200, but the following PUT request get 403

This is my server-side code responsible for AWS and its S3 service:

const AWS = require('aws-sdk');
const config = {
  accessKeyId: process.env.AWS_ACCESS_KEY_ID,
  secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
  region: process.env.AWS_BUCKET_REGION,
};
AWS.config.update(config);

const S3Bucket = new AWS.S3({
  signatureVersion: 'v4',
  params: { Bucket: process.env.AWS_BUCKET_NAME },
});

const uploadImage = async (fileData) => {
  // fileData contains `name` and `type` properties
  const Key = `images/${fileData.name}`;
  const params = {
    Bucket: process.env.AWS_BUCKET_NAME,
    Key,
    Expires: 15 * 60, // 15 minutes
    ContentType: fileData.type,
    ACL: 'public-read',
  };
  const url = await S3Bucket.getSignedUrlPromise('putObject', params);
  return url;
};

The IAM User from the code above (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY) has the following policy attached:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1418647210000",
            "Effect": "Allow",
            "Action": [
                "s3:Put*"
            ],
            "Resource": [
                "arn:aws:s3:::my-actual-bucket-name-here/*"
            ]
        }
    ]
}

My actual bucket has no Bucket policy set and has the following CORS configuration:

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
    <AllowedOrigin>*</AllowedOrigin>
    <AllowedMethod>HEAD</AllowedMethod>
    <AllowedMethod>GET</AllowedMethod>
    <AllowedMethod>PUT</AllowedMethod>
    <AllowedMethod>POST</AllowedMethod>
    <MaxAgeSeconds>3000</MaxAgeSeconds>
    <AllowedHeader>*</AllowedHeader>
</CORSRule>
</CORSConfiguration>

When I make a request from the browser to my server I get a signed URL in the response. Then I use this URL to perform a put request using the following code:

// `file` is a File class object (that inherits from `FilePrototype` which inherits from `BlobPrototype` that has the following attributes
// lastModified: 1556044130023
​// name: "profile.jpg"
​​// size: 788956
​​// type: "image/jpeg"
​​// uid: "rc-upload-1578069253604-2"
​​// webkitRelativePath: ""

const url = 'https://my-actual-bucket.s3.eu-central-1.amazonaws.com/images/profile.jpg?Content-Type=image%2Fjpeg&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=MYCREDENTIALCODE%2F20200103%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20200103T163418Z&X-Amz-Expires=900&X-Amz-Signature=b90ed9cbdfadc6401521f80f5d4a65e7d4182becd392ad274ffbe3405d626055&X-Amz-SignedHeaders=host%3Bx-amz-acl&x-amz-acl=public-read';
const response = await fetch(url, {
  method: 'PUT',
  body: file,
  headers: {
    'Content-Type': file.type,
  },
});

In my Network tab I can see an OPTIONS request that ends up returning 200, and a following PUT request that ends up with 403 saying:

<Error><Code>AccessDenied</Code><Message>Access Denied</Message><RequestId>BFBCD6D538B3EB6A</RequestId><HostId>BtQuuVJw63Ixvir1ghCu0QLq/FKORNSIyyIh9AoYhul1TnsaoZZ1V0p/FBooM/0HTNhM7ZSegM8=</HostId></Error>

Any idea what am I doing wrong here?

Answer 1

You need to add the S3:GetObject permission to your IAM policy. This permission is required because the user (in this case the application) is ultimately granting others permission to "read" (get) an object via a pre-signed URL. Therefore, it also needs to have the "read" (get) permission.