MYSQL injections: Are they a threat?
Can somebody tell my, what these attacks are about?


They're requests from bots fishing for vulnerabilities in your website.


  Was there a bug in Drupal making it vulnerable for those attacks?


Vulnerable to the specific attempts you've listed? Looking at the exact nature of the URLs, probably not. But there was, of course, Drupalgeddon once upon a time, so maybe.


  Is somebody else experiencing those attacks?


It's highly likely that they are. These attacks are usually orchestrated against as many potential victims as possible, and not built to target a single site. If the attacks you're experiencing were tailored, you would probably expect to see less generic and more Drupal-focused approaches.



You may wish to consider installing and configuring something like Fail2Ban to help with keeping the bots out.