Writing on his blog on Monday, Israeli researcher Nir Goldshlager said he discovered the password reset vulnerability while analyzing a Accellion deployment that is used, internally, by Facebook employees. Goldshlager used public knowledge of the Accellion platform to access a hidden account creation page for the Facebook deployment and create a new Facebook/Accellion account linked to his e-mail address.
After analyzing Accellion's password reset feature, he realized that — with that valid account — he could reset the password of any other Facebook/Accellion user with some cutting and pasting and a simple HTTP POST request, provided he knew the user's login e-mail address — effectively hijacking the account.
Goldshlager said he informed Facebook and that the hole has been patched by Facebook and Accellion. However, other Accellion customers using private cloud deployments of the product could still be vulnerable."