A Researcher Figured Out How To Reveal Any Phone Number Linked To a Google Account

A cybersecurity researcher was able to figure out the phone number linked to any Google account, information that is usually not public and is often sensitive, according to the researcher, Google, and 404 Media's own tests. From a report: The issue has since been fixed but at the time presented a privacy issue in which even hackers with relatively few resources could have brute forced their way to peoples' personal information. "I think this exploit is pretty bad since it's basically a gold mine for SIM swappers," the independent security researcher who found the issue, who goes by the handle brutecat, wrote in an email. [...] In mid-April, we provided brutecat with one of our personal Gmail addresses in order to test the vulnerability. About six hours later, brutecat replied with the correct and full phone number linked to that account. "Essentially, it's bruting the number," brutecat said of their process. Brute forcing is when a hacker rapidly tries different combinations of digits or characters until finding the ones they're after. Typically that's in the context of finding someone's password, but here brutecat is doing something similar to determine a Google user's phone number. Brutecat said in an email the brute forcing takes around one hour for a U.S. number, or 8 minutes for a UK one. For other countries, it can take less than a minute, they said. In an accompanying video demonstrating the exploit, brutecat explains an attacker needs the target's Google display name. They find this by first transferring ownership of a document from Google's Looker Studio product to the target, the video says. They say they modified the document's name to be millions of characters, which ends up with the target not being notified of the ownership switch. Using some custom code, which they detailed in their write up, brutecat then barrages Google with guesses of the phone number until getting a hit. Read more of this story at Slashdot.

Jun 9, 2025 - 17:40

A Researcher Figured Out How To Reveal Any Phone Number Linked To a Google Account

A cybersecurity researcher was able to figure out the phone number linked to any Google account, information that is usually not public and is often sensitive, according to the researcher, Google, and 404 Media's own tests. From a report: The issue has since been fixed but at the time presented a privacy issue in which even hackers with relatively few resources could have brute forced their way to peoples' personal information. "I think this exploit is pretty bad since it's basically a gold mine for SIM swappers," the independent security researcher who found the issue, who goes by the handle brutecat, wrote in an email. [...] In mid-April, we provided brutecat with one of our personal Gmail addresses in order to test the vulnerability. About six hours later, brutecat replied with the correct and full phone number linked to that account. "Essentially, it's bruting the number," brutecat said of their process. Brute forcing is when a hacker rapidly tries different combinations of digits or characters until finding the ones they're after. Typically that's in the context of finding someone's password, but here brutecat is doing something similar to determine a Google user's phone number. Brutecat said in an email the brute forcing takes around one hour for a U.S. number, or 8 minutes for a UK one. For other countries, it can take less than a minute, they said. In an accompanying video demonstrating the exploit, brutecat explains an attacker needs the target's Google display name. They find this by first transferring ownership of a document from Google's Looker Studio product to the target, the video says. They say they modified the document's name to be millions of characters, which ends up with the target not being notified of the ownership switch. Using some custom code, which they detailed in their write up, brutecat then barrages Google with guesses of the phone number until getting a hit.