In every pentest web there is several hidden and obvious places that might be vulnerable. This post is meant to be a checklist to confirma that you have searched vulnerabilities in all the posible places.
If the introduced data may somehow being reflected in the response, the page might be vulnerable to several issues.
Some of the mentioned vulnerabilities requires special conditions, others just require the content to be reflected. You can find some interesting polygloths to test quickly the vulnerabilities in:
If the functionality may be used to search some kind of data inside the backend, maybe you can (ab)use it to search arbitrary data.
When websocket, post message or a form allows user to perform actions vulnerabilities may arise.
Depending on the HTTP headers given by the web server some vulnerabilities might be present.
There are several specific functionalities were some workarounds might be useful to bypass them
Some functionalities will require the data to be structured on a very specific format (like a language serialized object or a XML). Therefore, it's more easy to identify is the application might be vulnerable as it needs to be processing that kind of data. Some specific functionalities my be also vulnerable if a specific format of the input is used (like Email Header Injections).
Functionalities that allow to upload files might be vulnerable to several issues. Functionalities that generates files including user input might execute unexpected code. Users that open files uploaded by users or automatically generated including user input might be compromised.
This vulnerabilities might help to exploit other vulnerabilities.