A researcher has disclosed the details of a two-factor authentication (2FA) vulnerability that earned him a $27,000 bug bounty from Facebook parent company Meta.
Gtm Manoz of Nepal discovered in September 2022 that a system designed by Meta for confirming a phone number and email address did not have any rate-limiting protection.
A fix was rolled out by Meta in October 2022 and the company highlighted Manoz’s findings in its annual bug bounty program report. The tech giant has paid out more than $16 million through its program since 2011, with $2 million awarded in 2022.
In a blog post published earlier this month, Manoz said he discovered the vulnerability while analyzing a new Meta Accounts Center page in Instagram. Here, users can add an email address and phone number to their Instagram account and the Facebook account linked to their Instagram. In order to verify the email address and phone number, users have to enter a six-digit code received via email or SMS.
The researcher’s analysis revealed that the system verifying the six-digit code did not have rate-limiting in place, which could have allowed an attacker to enter every possible code until they got the right one.
Specifically, a hacker would have needed to know the phone number assigned by the targeted user to their Instagram and Facebook account. By exploiting the vulnerability, the attacker could have obtained the six-digit verification code through a brute-force attack and assigned the victim’s phone number to an account they controlled.
This resulted in the phone number being removed from the victim’s Facebook and Instagram account and 2FA getting disabled due to security reasons — if a phone number is verified by another user, that user would be getting the SMS containing the 2FA code, and Meta is trying to prevent that.
Manoz showed that Facebook users did receive a notification when their phone number was removed due to being verified by a different person.
Based on the maximum potential impact of the vulnerability, Meta decided to pay out $27,200 for the researcher’s findings.
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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.
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