Sprint Defaults and the Jeep Hack: Could Basic Network Settings Have Prevented the Industry Uproar?

In mid-July, research into the security of a Jeep Cherokee was disclosed though a Wired article and subsequent Black Hat presentation. The researchers, Charlie Miller and Chris Valasek, found an exploitable vulnerability in the Uconnect entertainment system that operates over the Sprint cellular network. The vulnerability was serious enough to prompt a 1.4 million-vehicle recall from Chrysler.

In the Wired article, Miller and Valasek describe two important aspects of the vulnerability. First, they can target their exploit against a specific vehicle: “anyone who knows the car’s IP address can gain access from anywhere in the country,” and second, they can scan the network for vulnerable vehicles including a Dodge Ram, Jeep Cherokee, and a Dodge Durango. Both of these capabilities, to scan and target remotely through the cellular network, are necessary in order to trigger the exploit against a target vehicle.

While it’s really scary to think that a hacker anywhere in the country can drive your car off the road with the push of a button, the good news is that the cellular network has safeguards in place to prevent remotely interacting with phones and devices like Uconnect. For some inexplicable reason, Sprint disabled these safeguards and left the door wide open for the possibility of remote exploitation against the Uconnect cars. Had Sprint not disabled these safeguards, the Uconnect vulnerability would have just been another of several that require physical access to exploit and may not have prompted an immediate recall. 

The Gateway

Cellular networks are firewalled at the edge (Figure 1). GSM, CDMA and LTE networks are all architected a little differently, but each contains one of the following Internet gateways:

  • CDMA: Packet Data Serving Node (PDSN) in CDMA networks (Verizon and Sprint)
  • GSM: Gateway GPRS Support Node (GGSN) (T-Mobile or AT&T)
  • LTE: the responsibilities of the gateway are absorbed into multiple components in the System Architecture Evolution (SAE). All major Telcos in the US operate LTE networks.

Figure 1: Network layout

To keep things simple and generic, we’ll just call this component “the gateway.” Network connections only originate in one direction: outbound. You can think of the core network of your phone network as a big firewalled LAN, and it is not possible to gain access to a phone from outside the phone network (Figure 2). 

Figure 2: The attacker is blocked from outside the core network.

Miller was able to operate behind this firewall by tethering his laptop to a burner phone that was on the Sprint network (Figure 3).

But by default, phones are blocked from seeing each other as well. So even if the attacker knows the IP address of another phone on the network, the network won’t allow her to make a data connection to connect to that phone (Figure 4).  The network enforces this by what are called Access Point Names (APNs). 

Figure 3: Device-to-device was enabled for the car’s APN, enabling remote exploitation. Why?

Figure 4: Default configuration, device-to-device connections disabled. The attacker cannot access the target device from inside the firewall.

When a phone on the network needs to make a data connection, it provides anAPN to the network. If you want to view the APN settings in your personal phone you follow these instructions for iPhone or Android.  The network gateway uses the APN to determine how to allow your phone to connect to the Internet.  There are hundreds of APNs in every network, and your carrier uses APNs to organize how different devices are allocating data for billing purposes. In the case of Uconnect, all Uconnect devices operate on the Sprint network and use their own private APN.  APNs are really useful for third parties, like Uconnect, to sell a service that runs over a cellular network. So that each Uconnect user doesn’t need to maintain a line of service with Sprint, Uconnect is responsible for the data connection, and end users pay Uconnect for service, which runs through a private APN that was set up for Uconnect.

APNs are used extensively to isolate private networks for machine-to-machine systems like smart road signs and home alarm systems. If you’ve ever bought a soda from a vending machine with a credit card, the back end connection was using a private APN. 

Vulnerabilities caused by misconfigured APNs are not new; the APN of the bike-sharing system in Madrid was hacked just last summer. These bike-sharing systems need device-to-device access because technicians perform maintenance on these machines via remote desktop.  


There is no obvious reason for Uconnect to need remote administration. Why then are device-to-device connections allowed for the Uconnect APN, especially since it opens the door to a remote access exploit?  We will probably never know, because six days after the Wired story was published, Miller tweeted that Sprint had blocked phone-to-car traffic as well as car-to-car traffic. What this really means is that Sprint disabled internal traffic for the Uconnect APN. The remote access vector was closed.

The fact that Sprint made this change so quickly suggests that device-to-device traffic was not necessary in the first place, which leads us to two conclusions: 1) Had Sprint simply left device-to-device traffic disabled, the Jeep incident would have required physical access and not have been any more of a story than the Ford Escape story in 2013, or 2) More seriously, if the story hadn’t attracted mainstream media attention, Chrysler might not have taken the underlying vulnerability as seriously, and the fix would have rolled out much later, if ever. 

Security shouldn’t be a function of the drama circus that surrounds it.


Firewall icon created by Yazmin Alanis from the Noun Project
Pirate Phone icon created by Adriana Danaila from the Noun Project
Pickup truck icon created by Jamie M. Laurel from the Noun Project