AWS S3 CORS 403 Error with OPTIONS request

Question

I am trying to access a html file which reside in the S3 from an ajax request and I got 403 error.

I read the AWS online that if I do such thing, I need to setup AWS CORS rules to fix the 403 error.

However, I have been trying two days and I don't have any luck. Here is my CORS configuration:

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

And my HTTP request looks like:

Accept  text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding gzip, deflate
Accept-Language en-US,en;q=0.5
Access-Control-Request-He...    x-csrftoken
Access-Control-Request-Me...    GET
Connection  keep-alive
Host    xxxxxxxxx.cloudfront.net
Origin  http://localhost:8000
User-Agent  Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0

Can anyone help me to see what I have missed?

Thanks!

Answer 1

For those who came here for 403 on OPTIONS request of cross origin s3 access and didn't find what they were looking for, perhaps my experience with this can help.

tldr; browsers are designed to set the origin to null on 302 redirects from a different origin

I also experienced a CORS issue on the preflight request to a resource on a bucket, a resource which was otherwise available if browsed to directly.

I had CORS configured on the bucket with the proper accepted headers and origin. Something like the following.

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
    <AllowedOrigin>http://localhost:8080</AllowedOrigin>
    <AllowedMethod>GET</AllowedMethod>
    <AllowedMethod>HEAD</AllowedMethod>
    <MaxAgeSeconds>3000</MaxAgeSeconds>
    <AllowedHeader>authorization</AllowedHeader>
</CORSRule>
</CORSConfiguration>

I then received an error along the lines of

Access to XMLHttpRequest at 'https://[REDACTED].s3.amazonaws.com/[REDACTED]?AWSAccessKeyId=[REDACTED]' (redirected from '[REDACTED]') from origin 'null' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

After inspecting the request headers, it was clear that the one suspect thing was the Origin having a value of "null".

Access-Control-Request-Headers: authorization
Access-Control-Request-Method: GET
Origin: null
Referer: [REDACTED]
User-Agent: [REDACTED]

As it turns out, browsers are designed to set the origin to null on 302 redirects from a different origin due to security issues. More info here.

There is no fix to this issue other than to not do a redirect. I had to redesign the backend resource that was doing a redirect to instead provide a link for direct access to the s3 bbject.