# Test Cloud Storage

|ID          |
|------------|
|WSTG-CONF-11|

## Summary

Cloud storage services allow web applications and services to store and access objects in the storage service. Improper access control configuration, however, may lead to the exposure of sensitive information, data tampering, or unauthorized access.

A known example is where an Amazon S3 bucket is misconfigured, although the other cloud storage services may also be exposed to similar risks. By default, all S3 buckets are private and can be accessed only by users who are explicitly granted access. Users can grant public access not only to the bucket itself but also to individual objects stored within that bucket. This may lead to an unauthorized user being able to upload new files, modify or read stored files.

## Test Objectives

- Assess that the access control configuration for the storage services is properly in place.

## How to Test

First, identify the URL to access the data in the storage service, and then consider the following tests:

- read unauthorized data
- upload a new arbitrary file

You may use curl for the tests with the following commands and see if unauthorized actions can be performed successfully.

To test the ability to read an object:

```bash
curl -X GET https://<cloud-storage-service>/<object>
```

To test the ability to upload a file:

```bash
curl -X PUT -d 'test' 'https://<cloud-storage-service>/test.txt'
```

In the above command, it is recommended to replace the single quotes (') with double quotes (") when running the command on a Windows machine.

### Testing for Amazon S3 Bucket Misconfiguration

The Amazon S3 bucket URLs follow one of two formats, either virtual host style or path-style.

- Virtual Hosted Style Access

```text
https://bucket-name.s3.Region.amazonaws.com/key-name
```

In the following example, `my-bucket` is the bucket name, `us-west-2` is the region, and `puppy.png` is the key-name:

```text
https://my-bucket.s3.us-west-2.amazonaws.com/puppy.png
```

- Path-Style Access

```text
https://s3.Region.amazonaws.com/bucket-name/key-name
```

As above, in the following example, `my-bucket` is the bucket name, `us-west-2` is the region, and `puppy.png` is the key-name:

```text
https://s3.us-west-2.amazonaws.com/my-bucket/puppy.png
```

For some regions, the legacy global endpoint that does not specify a region-specific endpoint can be used. Its format is also either virtual hosted style or path-style.

- Virtual Hosted Style Access

```text
https://bucket-name.s3.amazonaws.com
```

- Path-Style Access

```text
https://s3.amazonaws.com/bucket-name
```

#### Identify Bucket URL

For black-box testing, S3 URLs can be found in the HTTP messages. The following example shows a bucket URL is sent in the `img` tag in an HTTP response.

```html
...
<img src="https://my-bucket.s3.us-west-2.amazonaws.com/puppy.png">
...
```

For gray-box testing, you can obtain bucket URLs from Amazon's web interface, documents, source code, and any other available sources.

#### Testing with AWS-CLI

In addition to testing with curl, you can also test with the AWS command-line tool. In this case `s3://` URI scheme is used.

##### List

The following command lists all the objects of the bucket when it is configured public:

```bash
aws s3 ls s3://<bucket-name>
```

##### Upload

The following is the command to upload a file:

```bash
aws s3 cp arbitrary-file s3://bucket-name/path-to-save
```

This example shows the result when the upload has been successful.

```bash
$ aws s3 cp test.txt s3://bucket-name/test.txt
upload: ./test.txt to s3://bucket-name/test.txt
```

This example shows the result when the upload has failed.

```bash
$ aws s3 cp test.txt s3://bucket-name/test.txt
upload failed: ./test2.txt to s3://bucket-name/test2.txt An error occurred (AccessDenied) when calling the PutObject operation: Access Denied
```

##### Remove

The following is the command to remove an object:

```bash
aws s3 rm s3://bucket-name/object-to-remove
```

## Tools

- [AWS CLI](https://aws.amazon.com/cli/)

## References

- [Working with Amazon S3 Buckets](https://docs.aws.amazon.com/AmazonS3/latest/dev/UsingBucket.html)
- [flAWS 2 - Learn AWS Security](http://flaws2.cloud)
- [curl Tutorial](https://curl.se/docs/manual.html)