In the wake of a scandal involving third-party companies leaking or selling precise, real-time location data on virtually all Americans who own a mobile phone, the four major wireless carriers have responded to requests from a U.S. senator for more details about how the carriers are managing access to this extremely sensitive information. While three out of four providers said they had cancelled data sharing agreements with some of the offending companies, only one — Verizon — pledged to terminate all of them and initiate a wholesale review of their location data-sharing practices.

At issue are companies known in the wireless industry as “location aggregators,” entities that manage requests for real-time customer location data for a variety of purposes, such as roadside assistance and emergency response. These aggregators are supposed to obtain customer consent before divulging such information, but several recent incidents show that this third-party trust model is fundamentally broken.

On May 10, 2018, The New York Times broke the story that a little-known data broker named Securus was selling local police forces around the country the ability to look up the precise location of any cell phone across all of the major U.S. mobile networks.

Then it emerged that Securus had been hacked, its database of hundreds of law enforcement officer usernames and passwords plundered. We also learned that Securus’ data was ultimately obtained from a company called 3Cinteractive, which in turn obtained its data through a California-based location tracking firm called LocationSmart.

On May 17, KrebsOnSecurity broke the news of research by Carnegie Mellon University PhD student Robert Xiao, who discovered that a LocationSmart try-before-you-buy opt-in demo of the company’s technology was wide open — allowing real-time lookups from anyone on anyone’s mobile device — without any sort of authentication, consent or authorization.

LocationSmart disabled its demo page shortly after that story. By that time, Sen. Ron Wyden (D-Ore.) had already sent letters to AT&T, Sprint, T-Mobile and Verizon, asking them to detail any agreements to share real-time customer location data with third-party data aggregation firms.

AT&T, T-Mobile and Verizon all said they had terminated data-sharing agreements with Securus. In a written response (PDF) to Sen. Wyden, Sprint declined to share any information about third-parties with which it may share customer location data, and it was the only one of the four carriers that didn’t say it was terminating any data-sharing agreements.

T-Mobile and Verizon each said they both share real-time customer data with two companies — LocationSmart and another firm called Zumigo, noting that these companies in turn provide services to a total of approximately 75 other customers.

Verizon emphasized that Zumigo — unlike LocationSmart — has never offered any kind of mobile location information demo service via its site. Nevertheless, Verizon said it had decided to terminate its current location aggregation arrangements with both LocationSmart and Zumigo.

“Verizon has notified these location aggregators that it intends to terminate their ability to access and use our customers’ location data as soon as possible,” wrote Karen Zacharia, Verizon’s chief privacy officer. “We recognize that location information can provide many pro-consumer benefits. But our review of our location aggregator program has led to a number of internal questions about how best to protect our customers’ data. We will not enter into new location aggregation arrangements unless and until we are comfortable that we can adequately protect our customers’ location data through technological advancements and/or other practices.”

In its response (PDF), AT&T made no mention of any other company besides Securus. AT&T indicated it had no intention to stop sharing real-time location data with third-parties, stating that “without an aggregator, there would be no practical and efficient method to facilitate requests across different carriers.”

Sen. Wyden issued a statement today calling on all wireless companies to follow Verizon’s lead.

“Verizon deserves credit for taking quick action to protect its customers’ privacy and security,” Wyden said. “After my investigation and follow-up reports revealed that middlemen are selling Americans’ location to the highest bidder without their consent, or making it available on insecure web portals, Verizon did the responsible thing and promptly announced it was cutting these companies off. In contrast, AT&T, T-Mobile, and Sprint seem content to continuing to sell their customers’ private information to these shady middle men, Americans’ privacy be damned.”

Wyden’s letter asked the carriers to detail any arrangements they may have to validate that location aggregators are in fact gaining customer consent before divulging the information. Both Sprint and T-Mobile said location aggregators were contractually obligated to obtain customer consent before sharing the data, but they provided few details about any programs in place to review claims and evidence that an aggregator has obtained consent.

AT&T and Verizon each said they have processes for periodically auditing consent practices by the location aggregators, but that Securus’ unauthorized use of the data somehow flew under the radar.

AT&T noted that it began its relationship with LocationSmart in October 2012 (back when it was known by another name, “Locaid”).  Under that agreement, LocationSmart’s customer 3Cinteractive would share location information with prison officials through prison telecommunications provider Securus, which operates a prison inmate calling service.

But AT&T said after Locaid was granted that access, Securus began abusing it to sell an unauthorized “on-demand service” that allowed police departments to learn the real-time location data of any customer of the four major providers.

“We now understand that, despite AT&T’s requirements to obtain customer consent, Securus did not in fact obtain customer consent before collecting customers’ location information for its on-demand service,” wrote Timothy P. McKone, executive vice president of federal relations at AT&T. “Instead, Securus evidently relied upon law enforcement’s representation that it had appropriate legal authority to obtain customer location data, such as a warrant, court order, or other authorizing document as a proxy for customer consent.”

McKone’s letter downplays the severity of the Securus incident, saying that the on-demand location requests “comprised a tiny fraction — less than two tenths of one percent — of the total requests Securus submitted for the approved inmate calling service. AT&T has no reason to believe that there are other instances of unauthorized access to AT&T customer location data.”

Blake Reid, an associate clinical professor at the University of Colorado School of Law, said the entire mobile location-sharing debacle shows the futility of transitive trust.

“The carriers basically have arrangements with these location aggregators that contractually say, ‘You agree not to use this access we provide you without getting customer consent’,” Reid said. “Then that aggregator has a relationship with another aggregator, and so on. So what we then have is this long chain of trust where no one has ever consented to the provision of the location information, and yet it ends up getting disclosed anyhow.”

Curious how we got here and what Congress or federal regulators might do about the current situation? Check out last month’s story, Why Is Your Location Data No Longer Private.