Facebook CSRF protection bypass which leads to Account Takeover.
This bug could have allowed malicious users to send requests with CSRF tokens to arbitrary endpoints on Facebook which could lead to takeover of victim’s accounts. In order for this attack to be effective, an attacker would have to trick the target into clicking on a link. Demonstration This is possible because of a vulnerable endpoint which takes another given Facebook endpoint selected by the attacker along with the parameters and make a POST request to that endpoint after adding the fb_dtsg parameter. Also this endpoint is located under the main domain www.facebook.com which makes it easier for the attacker to trick his victims to visit the URL. The vulnerable endpoint is: https://www.facebook.com/comet/dialog_DONOTUSE/?url=XXXX where XXXX is the endpoint with parameters where the POST request is going to be made (the CSRF token fb_dtsg is added automatically to the request body). This allowed me to make many actions if the victim visits this URLs. Some ...