Hackers abused Twitter API to match usernames to phone numbers

Twitter discloses a security incident involving third-parties that exploited its official API to match phone numbers with Twitter usernames.

On December 24, 2019 the company discovered that its API were exploited by a large network of fake accounts to match Twitter usernames to phone numbers. The company immediately suspended the involved accounts.

“On December 24, 2019 we became aware that someone was using a large network of fake accounts to exploit our API and match usernames to phone numbers. We immediately suspended these accounts” reads the statement published by Twitter.

“During our investigation, we discovered additional accounts that we believe may have been exploiting this same API endpoint beyond its intended use case.”

Twitter was informed of the abuse of Twitter API following a report from TechCrunch site. The post published by TechCrunch detailed how the security researchers Ibrahim Balic abused a Twitter API to match 17 million phone numbers to public usernames.

Balic provided TechCrunch with a sample of the phone numbers he successfully matched, in one case, TechCrunch was able to identify a senior Israeli politician using their matched phone number.

Twitter investigated the issue and discovered that the accounts involved in the incident were from a wide range of countries, the experts discovered that a high volume of requests was coming from IP addresses located within Iran, Israel, and Malaysia. 

Twitter speculates that it is possible that some of these IP addresses may have links to nation-state actors.

Twitter confirmed that the security incident only impacted Twitter users who enabled an option in their settings section to allow phone number-based matching.

“When used as intended, this endpoint makes it easier for new account holders to find people they may already know on Twitter. The endpoint matches phone numbers to Twitter accounts for those people who have enabled the “Let people who have your phone number find you on Twitter” option and who have a phone number associated with their Twitter account.” continues Twitter.

“People who did not have this setting enabled or do not have a phone number associated with their account were not exposed by this vulnerability,”

Twitter immediately implemented a number of changes to this endpoint to avoid future abuse of the API.

Pierluigi Paganini

(SecurityAffairs – Twitter API, hacking)

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