I had discovered a vulnerable in Facebook :

-----------| Threat Level :  Between medium and high
-------| Tested on : Windows 8 using Google chrome
---| The vuln is already reported but not closed yet

------------------| Description :

Hi I'm Hamza Belkhiat from Morocco , it was like a 3 weeks when i report it with full report including photos but someone in security team answer me and he told me that he had confused about it , i have answer him and i gave him an explanation's video
on YouTube and they don't answer me since there first khalil who found the wall vulnerable and now me ...etc

let's back to our subject :
the vulnerable is when you want to add mobile to your account to verify it , or you can add a new number to Facebook without any verification code , but with this vulnerable you can add any mobile number , what ever you want ( a valid or not valid number ) with just some codes you can add it without any difficulty.
Anyways this vulnerable is a big chance for spammers to verify their account and spam everybody that they want , because Facebook has a security Technique , any new account should be verify or it will be limited you can see that if you have create a new account but with this vulnerable , You could verify your account even it's new one , and Facebook could not close it.

----------------------| This is a video show you the prove : ( but not show you how to do it )