That's not obvious at all. If I receive json data that contains a property I'm not aware of, i don't reject the entire document for that reason. In the case of query strings, extra query parameters might be used by other parts of the stack besides yours, so rejecting the entire document because someone somewhere else is trying to pass information to itself is the wrong approach.
As a web developer, you’re the like the guy standing with a clipboard outside a fancy club checking if people requesting entry are allowed or not. Basically, level 1 security.
If someone is not on the list, your job is to default to declining them access, not granting them access assuming level 2 security will handle them at a deeper layer.
It’s possible that the teams you work with expect fuzzy behaviour from the website but that’s a choice, not a practice.
This is how the vast majority of websites work. The practical reason is obvious: when we model the behaviour our code depends on, we want to create the simplest possible model that allows our code to work as expected. Placing requirements on it that our code doesn't actually depend on is useless, unneeded, complexity.
> As a web developer, you’re the like the guy standing with a clipboard outside a fancy club checking if people requesting entry are allowed or not. Basically, level 1 security.
there is no security benefit to filtering out unneeded url parameters.
What about passing extra data to fill the server memory with either extra known junk or a script / executable to use with a zero day in an internal component or something.
To misuse the nightclub analogy: it’s like checking for bags not being larger than A4 and disallow knives and other weapons.
there is - security in depth.
If a url parameter would've been a vulnerability because something lower down the stack misinterprets it (and the param wasn't necessary for your app in the first place), then you've just left a window open for the exploit.
If the set of url params are known ahead of time (which i claim should be true), then you could make adding unknown params an error.
By assumption, you are using this url parameter. So you have a bug where you've forgotten to allow this parameter, which will quickly be discovered in your logs and fixed. Then the vulnerability, which you are thus far unaware of, will quickly be exposed. Those url parameters you are not using cannot hurt you.