While I was looking into my emails to unsubscribe from them, then there was mail from confluent. On copying the link, I found a subdomain https://sdr.confluent.io. Changing the id parameter allowed any user to be unsubscribed from confluent mails along with that it allowed content spoofing and after submitting on unsubscribing it redirected to the homepage. So after changing URL from the homepage to any website.

Content spoofing, also referred to as content injection, “arbitrary text injection” or virtual defacement, is an attack targeting a user made possible by an injection vulnerability in a web application

Open Redirects are invalidated redirects and forwards are possible when a web application accepts untrusted input that could cause the web application to redirect the request to a URL contained within untrusted input.

Insecure Direct Object Reference refers to when a reference to an internal implementation object is exposed to users without any proper access control setting.

Link:
https://sdr.confluent.io/api/mailings/1xxxx7/unsubscribe_html?id=1xxxx7&message=ALERT:%20THERE%20HAD%20BEEN%20A%20MASSIVE%20BREACH%20AT%20OUR%20DATA%20CENTER.%20KINDLY%20UNSUBSCRIBE%20AND%20RE-REGISTER%20AT%20https://xxx.org&org=03cc2586-0cbc-479a-a28c-25882d14226f&sig=tzKGVFwyxtfzk1KYmkZHOHWFWd4S7Bjnt-qePZ6RlmQ%3D&unsubscribe_redirect_url=https%3A%2F%2Fwww.openbugbounty.org
It is vulnerable to Content Spoofing and URL redirect and idor.

Parameters vulnerable:
id= xxxxxx
message= xxxxxx
unsubscribe_redirect_url= https://examplexxx.com

Any malicious User can Unsubscribe anyone that has subscribed to emails by simply brute-forcing id parameter and it can be used to spoof the message to click on unsubscribe which will redirect to a malicious website.

Since it was a simple business logic error. So, providing id and message field and replacing with a signature so that input cannot be provided externally.

Since this issue was a third party issue as mail is under managed services and didn’t come directly under confluent but organization responsible for the issue confirmed that the issue has been remediated and the fix has been implemented.

https://hackerone.com/reports/201314
https://hackerone.com/reports/230328
https://www.bugcrowd.com/how-to-find-idor-insecure-direct-object-reference-vulnerabilities-for-large-bounty-rewards/

06/29/2018: Discovered and reported to the confluent team
06/29/2018: Bug confirmed
08/17/2018: Bug fixed by the third party and confirmed by theconfluent team
08/30/2018: Confirmed for public disclosure
28/09/2018: Published POC

#justmorpheus