– Updated 10/25/2018 – The NYT is reporting that China and Russia are spying on Trump via his unsecured iPhone. NYT says that though intercepted calls, likely related to SS7 the Chinese have pieced together a list of the people with whom Mr. Trump regularly speaks in hopes of using them to influence the president, the officials said. Among those on the list are Stephen A. Schwarzman, the Blackstone Group CEO, and Steve Wynn, the former Las Vegas casino magnate.
A number of outlets are speculating that the Chinese are using the known SS7 flaw to spy on the president’s iPhone. I have written about the problems with SS7 a number of times since 2016 and now the chicken has come home to roost.
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Trump recently bragged that he gave the North Korean dictator his personal cell number. If that is true, he has created a major national security exposure. Karsten Nohl, chief scientist at the firm Security Research Labs, who researches cell network attacks told Wired, “Absolutely that is a problem.” He says hackers can abuse flaws in Signaling System 7 to listen in on someone’s phone calls, intercept their text messages, and track their location.
If North Korean intelligence isn’t already tracking Trump’s phones through malware, a direct phone number could give them a way in. The SS7 attacks can give hackers relatively easy access to calls and texts, and location data. Wired points out that North Korea has proven itself as an adversary willing to hack and manipulate systems around the world for its financial or intelligence gain—it was responsible both for the 2014 hack of Sony and 2017’s WannaCry ransomware outbreak – SS7 hacking is likely no exception.
The telecom industry and U.S.government have done very little to plug the SS7 hole. Senator Ron Wyden, a Democrat from Oregon and a senior member of the Senate Select Committee on Intelligence, has been tracking the SS7 issue for several years. He has sent letters to FCC Chairman Ajit Pai, asking for answers on SS7 security and details about how many network providers have been breached through SS7. Mr. Wyden wrote, “I’ve spent the past year fighting to reveal what a terrible job the telephone companies and FCC are doing at protecting Americans from being spied on, tracked, or scammed.”
Attackers used SS7 to get customer data
Mr. Wyden said he had been told by a big-name mobile network that malicious attackers are believed to have used SS7 to obtain US customer data. DHS confirmed reports of “nefarious” types leveraging SS7 to spy on American citizens by targeting their calls, text messages, and other information.
So what is SS7?
The Signaling System 7 (SS7) network is fundamental to cellphones operations, but its security design relies entirely on trust. The protocol does not authenticate messages; anyone with access to SS7 can send a routing message, and the network will make it. Now as SS7 network operators are opening the SS7 network to third-party access, vulnerabilities are being exposed and attacked initially by governments and now criminals.
Since 1975, over 800 telecommunications companies around the world use SS7 to ensure their networks interoperate. SearchNetworking.com defines the Signaling System 7 (SS7) as an international telecommunications standard that describes how network elements in a public switched telephone network (PSTN) exchange information over a digital signaling network.
SS7 control messages
SS7 control messages contain routing, congestion, and authentication information.
- SS7 routing deals with: How do I send a call to 313-555-1234?
- Congestion – What to do if the route to a network point is crowded.
- Authentication – Confirms that the caller is a valid subscriber and lets the call set up continue.
They explain that SS7 consists of a set of reserved or dedicated channels known as signaling links. There are three kinds of network points signaling points:
- Service Switching Points (SSPs) originate or terminate a call and communicate with SCPs to determine how to route a call or set up and manage some special feature.
- Signal Transfer Points (STPs) are packet switches that route traffic on the SS7 network.
- Service Control Points (SCPs) SCPs and STPs are usually mated so that service can continue if one network point fails.
SS7 out-of-band signaling (control) information travels on a separate, dedicated 56 or 64 Kbps channel and not within the same channel as the telephone call. Historically, the signaling for a telephone call has used the same voice circuit that the telephone call traveled on. Using SS7, telephone calls can be set up more efficiently and special services such as call forwarding and wireless roaming service are easier to add and manage. SS7 is used for:
- Setting up and managing the connection for a call,
- Tearing down the connection when the call is complete
- Billing,
- Managing features such as:
- call forwarding,
- calling party name and number display,
- three-way calling,
- Toll-free (800 and 888) and toll (900) calls
- 911 emergency service calls in the US, and,
- Other Intelligent Network (IN) services.
- Wireless as well as wireline call service including:
- Mobile telephone subscriber authentication,
- Personal communication service (PCS) and,
- Roaming,
- SMS messages.
Within SS7, SMS messages are sent on the same channels and infrastructure as SS7 uses to control the core of the telephone networks.
When an SMS message is sent from an SMS-capable cell phone, the message is handled no differently than a normal call setup: it moves from the cell phone to a base station to a Mobile Switching Center (MSC).
From the mobile switching center, the SMS message moves inside the SS7 network to the Short Messaging Service Center (SMSC), a standard part of the network. The SMSC queries the Home Location Register (HLR) to find out where the recipient of the message is and whether he or she is switched on to receive a message. If not, the SMSC stores the message until it can be delivered.
Mobile Switching Center (MSC) — The MSC is the equivalent of the local switch inside the mobile network. It provides very similar services to a switch, but uses virtual circuits over radio channels instead of physical voice circuits. One variation on the MSC is the Gateway Mobile Switching Center (GMSC) which routes calls into and out of the network and will not have phones locally registered.
Visitor Location Register (VLR) — The VLR is the database attached to an MSC that keeps track of all the phones currently “registered” to it, informing other nodes of status changes, and checking authentication information.
Short Message Service Center (SMSC) —The SMSC is the clearinghouse for SMS messages on an SS7 network and provides store-and-forward services.
Home Location Register (HLR) — HLR is a core database that keeps track of subscribers. It contains information on the current account status and provides authorization information for billing. When a call or SMS is trying to reach a subscriber, this is the node that is queried to find out where in the network that subscriber actually is.
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Mr. Nohl told Motherboard SS7 is, “probably the weakest link in our digital protection chain.” CTIA, the telecom lobbying arm, denies there is a problem with SS7. CTIA told DHS that the SS7 flaws are “perceived shortcomings.” They also said that talking about SS7 attacks is “unhelpful.” CTIA, practicing “security through obscurity,” claimed that talking about the issues may help hackers.
This is a mess. Contact your senator and representative in D.C. and tell them to support Senator Wyden, efforts to force the FCC to deal with the SS7 flaws.
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Ralph Bach has been in IT long enough to know better and has blogged from his Bach Seat about IT, careers, and anything else that catches his attention since 2005. You can follow him on LinkedIn, Facebook, and Twitter. Email the Bach Seat here.
SMS authentication is one of the major security mechanisms for services like 
CBS correspondent 
Representative Lieu has called for a congressional investigation of the vulnerabilities in SS7. He wrote that “The applications for this vulnerability are seemingly limitless, from criminals monitoring individual targets to foreign entities conducting economic espionage on American companies to nation states monitoring U.S. government officials.” Lieu said the investigation should be conducted by the