Attackers likely sponsored by a nation state used an extensive network of Twitter accounts to match phone numbers to usernames by abusing an existing API and going well beyond its intended use, the social network has said.
A Twitter feature allows new people joining the social network to find users they know by using their phone number. Of course, this is only possible if users associate their phone number to their Twitter account.
Attackers wielding a large number of existing Twitter accounts were exploiting this feature in an effort to match usernames to phone numbers. While not all requests came from the same places, many were from IPs in Iran, Israel and Malaysia, and it’s believed that they might be connected to state-sponsored actors.
“When used as intended, this endpoint makes it easier for new account holders to find people they may already know on Twitter,” explained the company on its blog. 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.”
“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 suspended all accounts involved in this operation and altered the feature so the API can’t be used in this manner anymore. The investigation started on December 24, 2019, and it took the company a few weeks.
Users don’t have to do anything extra right now as the vulnerability that allowed attackers to match names and phone numbers was fixed.