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T-Mobile website bug reportedly exposed private customer account details

Brenda Stolyar
t-mobile

Due to a bug in T-Mobile’s website back in April, customers’ account information was left accessible for anyone to see, ZDnet reports. While the security flaw has since been fixed, personal information could have potentially been misused by anyone who knew where to look.

The subdomain — promotool.t-mobile.com — is a customer care portal for employees to access internal tools. But the bug allowed for it to be easily found through search engines and didn’t require a password to access the tools.

The flaw was due to a hidden API — it provided T-Mobile customer data by adding the customer’s cell phone number to the end of the web address. This data included a customer’s billing account number, postal address, and account information, such as the status of their bills, including if service for an account was suspended or a bill is past due. For some, customer account PINs and tax ID numbers were also accessible.

The API was pulled by T-Mobile a day after it was reported by security researcher Ryan Stevenson, who was also awarded a $1,000 bug bounty later. While it’s not clear how long the API was exposed, a spokesperson for T-Mobile told ZDnet that there’s no evidence any customer information was accessed.

This is isn’t the first time an issue like this has happened to T-Mobile. In October, a security flaw allowed hackers to gain access to similar information through a T-Mobile website. Hackers were able to obtain email addresses, account numbers, and more, simply by using the customer’s phone number.

The flaw was discovered by security researcher Karan Saini, and it allowed hackers to gain information that could then be used in a social engineering attack, as well as provided access to other personal information online. T-Mobile claimed the bug only affected a small amount of customers and that it was fixed within 24 hours of being discovered.

News of the most recent flaw comes a little less than a month after the merger with T-Mobile and Sprint was announced — which was also in April. While both carriers agreed on combining companies, we have yet to see whether the U.S. Justice Department will approve it.