Now a days every app has a module for notifying users through email. The same email module/service when written less carefully can lead to serious misuse by the attacker. Attacker can spam the inbox of any user when the app is vulnerable to this issue. Below is the example of vulnerable webapps test with explanation.
Suppose the reset password functionality is vulnerable to email bombing.
url – https://example.com/lost-password
Open it and you see a form to notify you by email. try putting email and send. Monitor and capture the request.
For now i take below headers:
POST /lost-password HTTP/1.1
User-Agent: Mozilla/5.0 (Windows NT 6.3; rv:36.0) Gecko/20100101 Firefox/36.04
Accept-Encoding: gzip, deflate, br
Cookie: lang=en; xyz
Looking at the header and body , we can see that their is no way for the web server to track user or to validate the genuine request. So we can replay the same request with different POST data using any client.