External Service Interaction (HTTP/DNS) on https://www.███ (██████████ parameter)

How it was found

Greetings, i've find a External service interaction (HTTP/DNS) on https://www.███████

External service interaction arises when it is possible to induce an application to interact with an arbitrary external service, 
such as a web or mail server. 
The ability to trigger arbitrary external service interactions does not constitute a vulnerability in its own right, 
and in some cases might even be the intended behavior of the application. 
However, in many cases, it can indicate a vulnerability with serious consequences.

In cases where DNS-based interactions can be triggered, it is normally possible to trigger interactions using other service types, 
and these are reported as separate issues.
 If a payload that specifies a particular service type (e.g. a URL) triggers only a DNS-based interaction, 
then this strongly indicates that the application attempted to connect using that other service, 
but was prevented from doing so by egress filters in place at the network layer. 
The ability to send requests to other systems can allow the vulnerable server to be used as an attack proxy. 
By submitting suitable payloads, an attacker can cause the application server to attack other systems that it can interact with. 
This may include public third-party systems, internal systems within the same organization, 
or services available on the local loopback adapter of the application server itself. Depending on the network architecture, 
this may expose highly vulnerable internal services that are not otherwise accessible to external attackers.

https://portswigger.net/kb/issues/00300200_external-service-interaction-dns

Full link : https://www.██████/█████

POST Request :

████████&MONTH=01&LNAME=frenchvlad&PHONE=555-555-0199&EDULVL=10&STATE=AL&EMAILFLAG=on&submitButton=Submit+Audition+Request&[email protected]&[email protected]&██████=http://bcrxn9tx1eboqdat33ghligdv41upj.burpcollaborator.net/?Winterville&[email protected]&INST1MOS=Bass+Guitar&CITY=Winterville&YEAR=2003&INST1YRS=2+TO+5&DAY=01&CITIZEN=R

my payload : █████████=http://bcrxn9tx1eboqdat33ghligdv41upj.burpcollaborator.net/?Winterville

Proof (DNS) :

██████

Proof (HTTP) :

█████

best regards, frenchvlad

Impact

We can use the weakness as a attack proxy to DDOS all Internal/external web conatiners, also could be amplified too