Yea, it's people throwing in checks for cases that should never happen, but probably have saved a lot of money and time for people who were running those products.
Thankfully, most of these I've seen in the first four pages are for things marked as a web shell, or a security scanner, etc, so it's purposeful and not meant for serious webapp use.
Still, kind of scary to see. It's like a listening netcat piping to bash in a loop. Sure there should be a firewall in front...
It looks like the vast majority are from forks of PHP Vulnerability Hunter, and a few more are from other vulnerability tests. So I guess this isn't actually that common?
There is a simple Google search that allows you to find thousands of websites that do this. Which I won't put since it essential gives you a list of websites ripe for take over.
The function eval[1] evaluates a string as code. The special variable $_GET[2] contains HTTP GET variables, which may be freely set by a remote user.
So if your PHP file executes eval($_GET['code']), then arbitrary folks can submit whatever code they want as a parameter -- as in /index.php?code=blah -- and have your webserver run it for them.
$_GET is a magic super global in PHP that contains all of the GET parameters of a request. Doing something like eval($_GET['code']); means you're essentially allowing a user to execute arbitrary code passed in through the URL. Not the safest thing to do...
It evaluates as PHP code the contents of the URL parameter named "code".
Although it seems like most hits are from PHP Vulnerability Hunter -- an automated whitebox fuzz testing tool capable of detected several classes of vulnerabilities in PHP web applications.
