Facebook has fixed a security flaw that allowed an attacker to take over any user’s account by abusing the social network’s password-reset mechanism.
The bug, discovered by Bangaluru-based researcher Anand Prakash, was found in Facebook sites used for beta-testing new features, and could have allowed straightforward access to any account.
Facebook allows anyone to reset the password for any account by entering the user’s telephone number or email address into a password recovery system. The site then sends a six-digit code to the user’s mobile phone that can be used to gain access to the account and set a new password.
Prakash found that two Facebook sites used for testing new features didn’t limit the number of times a user could enter an incorrect code. That meant a malicious user could write a simple script that kept guessing the code until it hit on the right one.
“I tried to takeover my account… and was successful,” he wrote. “I could then use the same password to login in the account.”
Facebook’s main website limited the number of incorrect guesses, Prakash noted.
He notified Facebook of the flaw on 22 February, and a fix was in place the next day. He said he received a bounty earlier this month.
Facebook’s bug bounty programme paid out about $936,000 last year, less than the $1.3m paid in 2014, but the social network said the bugs it was informed of were more serious than previously.
In February of last year a researcher from Tamil Nadu was awarded $12,500 for discovering a flaw that allowed users to delete photo albums belonging to other users.
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It is hard to believe Developers at FB missed out such a simple thing. I feel this was a backdoor as then an account be accessed. Thanks to Prakash, this backdoor stands exposed. Though I would not be surprised if there are other backdoors. Also storing email address /phone number in a format that can be retrieved by FB is the biggest backdoor by itself as anytime FB wants to access your account, all they need to do is replace your original email address/phone with something else they have access to.
To do away with this backdoor, FB should stop using email/phone numbers to retrieve passwords and instead use other alternatives where the password is not sent or generated using a personal identity but by a combination of identities that only the user knows but which is never stored on FB servers.
If FB is listening, I can help.