Whenever a user is asked to provide input, the program should expect errors. This is true for almost any language and almost any case; you should protect your MySQL code from sql-injections, your php input fields from scripts, your javascript from infinite loops, your java code from non-fitting variable type.

cURL is a PHP library that’s meant to safely retrieve remote data. The term ‘safely’ is a relative one, of course, depending on what you do with it. But since cURL doesn’t generally execute the fetched data, it is considered much safer than many other options.