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.