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Friday, May 17, 2024

A 5G Shortcut Leaves Most Phones Exposed to Stingrays

In North America and many other parts of the world, high-speed 5G mobile data networks dangled just out of reach for years. But as 5G coverage becomes ubiquitous, the rollout comes with an important caveat. Even if your phone says it's connected to the next-generation wireless standard, you may not actually be getting all of the features 5G promises—including defense against so-called stingray surveillance devices

To get 5G out to the masses quickly, most carriers around the world deployed it in something called “non-standalone mode” or “non-standalone architecture.” The approach essentially uses existing 4G network infrastructure as a jumping off point to put out 5G data speeds before the separate, "standalone" 5G core is built. It's like starting your cake-decorating business out of your cousin's ice cream shop while you renovate a new storefront three blocks away. 

You may see where this is going. As long as your 5G connection is in non-standalone mode, a lot of what you're getting is still actually 4G, complete with security and privacy weaknesses that actual 5G aims to address.

“It's a false sense of security,” says Ravishankar Borgaonkar, a research scientist at the Norwegian tech analysis firm SINTEF Digital and associate professor at University of Stavanger. “Currently a lot of the 5G deployed all over the world doesn’t actually have the protection mechanisms designed in 5G. You're getting the high speed connection, but the security level you have is still 4G."

In practice, that means one of 5G's top-billed privacy benefits—the ability to stymie stingray surveillance—does not yet apply for most people. Also known as "IMSI catchers" for the “international mobile subscriber identity” number assigned to every cell phone, stingrays act like legitimate cell towers and trick devices into connecting. From there, the tools use IMSI numbers or other identifiers to track the device, and even listen in on phone calls. Stingrays are a popular choice among US law enforcement; they were a reportedly common presence at many of last summer's anti-police brutality protests. To prevent that sort of monitoring, 5G is built to encrypt IMSI numbers.

Borgaonkar and fellow researcher Altaf Shaik, a senior research scientist at TU Berlin, found that major carriers in Norway and Germany are still putting out 5G in non-standalone mode, which means that those connections are still susceptible to stingrays. The two presented at the Black Hat security conference in Las Vegas last week. 


In the United States, T-Mobile is the farthest along in rolling out its standalone network. The company was the first to begin mass-deployment in August 2020. Verizon and AT&T have taken longer to transition and are still working on switching to high speed 5G in general. Verizon told WIRED that it is on track for “full commercialization” of 5G standalone mode by the end of 2021. AT&T says that it began “limited SA deployments” late last year, and that it will scale up “when the ecosystem is ready.”

A February study by the mobile network analytics firm OpenSignal found that at the beginning of 2021 US mobile users spent about 27 percent of their time on non-standalone mode 5G and less than six percent of their time on standalone mode connections.

While the distinctions between the types of 5G matter a great deal, there's no easy way to tell whether you're on a standalone network just by looking at your phone. Android users can download apps that analyze a device's network connection and can flag non-standalone mode, but that's an onerous extra step. And those tools are less common on iOS because of Apple's app restrictions.

The security benefits you miss while on a non-standalone 5G network extend beyond stingrays. You're potentially susceptible to tracking, eavesdropping, and so-called “downgrade attacks” that push target devices onto older, more vulnerable data networks like 3G. And none of this gets communicated to mobile data users, despite enhanced security features being a key 5G selling point.

The inherent challenge of implementing a massive infrastructure overhaul is the key issue, says Syed Rafiul Hussain, a mobile network security researcher at Pennsylvania State University. Even when 5G standalone mode is deployed in most places, he says, carriers will still run parallel 4G and 3G infrastructure as well that could continue to enable some stingray attacks. 

“As long as we need seamless connectivity, continuous connectivity, we'll need backward- compatibility using 4G,” he says. “4G stingray attacks, downgrading, man-in-the-middle attacks—those will exist for years even though we have 5G. And trying to move away from non-standalone mode to standalone mode everywhere will take some time.”

So far 90 network operators in 45 countries have committed to making the switch to standalone mode, says Jon France, head of industry security at the telecom standards body GSMA.

“The full picture, the full protections of 5G security come over time and do require the standalone to gain full benefit,” he says. “We’re seeing the initial deployments which are already bringing the core benefits of low latency, high data transfers through the non-standalone method. That still has a 4G core in it, it’s the brain of the network, and until we get to a 5G brain in standalone mode we won’t get all of the security benefits."

The industry can't languish in non-standalone mode, says SINTEF Digital's Borgaonkar. He suggests that smartphone vendors be required to build in options so users can set which types of mobile data networks they want their phone to connect with. Similar to roaming options, you could turn 2G or 5G non-standalone mode or any other iteration off most of the time when you don't want to risk being unintentionally bumped onto it.

“As the end user I don’t have any option to only get 5G standalone mode,” Borgaonkar says. “If 2G is not secure why can't I stop my phone from connecting to 2G? There is no requirement or coordination among the vendors about giving users these options—giving them the freedom to choose privacy.”

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