Fix: added information about query parameters validation

[IgorSasovets]

No description provided.

[PauloASilva]

Hi @IgorSasovets,
First of all thanks for your contribution!

By mistake, I suggested adding your changes to the
2019/en/src/0xa3-improper-data-filtering.md file: I should have written
2019/en/src/0xa4-lack-of-resources-and-rate-limiting.md. Can you please move
your changes to the appropriate file?

I also have two suggestions to improve your attack scenario:

• Remove reference to "MEAN stack": we want to keep this document agnostic and
  this same scenario is also valid for other stacks.
• "it causes performance issues": add one or more examples of what can cause
  such performance issues e.g. database timeout, memory exhaust, ...

Cheers,
Paulo A. Silva

[IgorSasovets]

Hi, @PauloASilva !

I added suggested changes. Please take a look at them.

Best regards,
Ihor