Tag Archive for SS7

Scary SS7 Flaw Strikes Banks

Scary SS7 Flaw Strikes BanksLost in last month’s hub-bub over WannaCry ransomware was the revelation that hackers had successfully exploited the SS7 “flaw” in January 2017. In May reports surfaced that hackers were able to remotely pilfer German bank accounts by taking advantage of vulnerabilities in Signaling System 7 (SS7). SS7 is a standard that defines how to public phone system talks to itself to complete a phone call.

Telephone system Signaling System 7 The high-tech heist was initially reported by the German newspaper Süddeutsche Zeitung (auf Deutsch). The attack was  a sophisticated operation that combined targeted phishing emails and SS7 exploits to bypass two-factor authentication (2FA) protection. This is the first publicly known exploit of SS7 to intercept two-factor authentication codes sent by a bank to confirm actions taken by online banking customers.

According to ars technica the attack began with traditional bank-fraud trojans. These trojans infect account holders’ computers and steal the passwords used to log in to bank accounts. From there, attackers could view account balances, but were prevented from making transfers without the one-time password the bank sent as a text message. After stealing the necessary login details via phishing emails, the perpetrators leveraged the SS7 flaw to intercept the associated mTAN (mobile transaction authentication numbers) authentication codes sent to the victims — messages notifying them of account activity — to validate the transactions and remain hidden, investigators say.

Central office equipmentGerman Telecommunications giant O2-Telefonica confirmed details of the SS7-based cyber attacks to the newspaper. Ars says, in the past, attackers have obtained mTANs by obtaining a duplicate SIM card that allows them to take control of the bank customer’s phone number. SS7-facilitated compromises, by contrast, can be done remotely on a much larger quantity of phone numbers.

O2 Telefonica confirmed to Help Net Security that the attackers were able to gain access to the network of a foreign mobile network operator in January 2017. The attackers likely purchased access to the foreign telecommunications provider – this can apparently be done for less than 1,000 euros – and have set up call and SMS forwarding.

Ford Road CO in Dearborn Mi is the Oregon officeTwo-factor authentication (2FA) is a security process in which the user provides two authentication factors to verify they are who they say they are.  2FA provides an extra layer of security and makes it harder for attackers to gain access to a person’s devices and online accounts, because knowing the victim’s password alone is not enough to pass the authentication check. Two-factor authentication has long been used to control access to sensitive systems and data, and online services are increasingly introducing 2FA to prevent their users’ data from being accessed by hackers who have stolen a password database or used phishing campaigns to get users’ passwords.

News of the incident prompted widespread concern online. Security advocates railed against the popular and continuous use of text messages to authenticate account information while growing evidence suggests that SS7 is an unsafe channel to deliver such data. Security experts told ars that the same SS7-centric hacking techniques used against German banks will become increasingly prevalent in the future, forcing organizations to reconsider how they authenticate user activity.

Cris Thomas, a strategist at Tenable Network Security warns in the article:

Two-factor authenticationWhile this is not the end of 2FA, it may be the end of 2FA over SS7, which comprises a majority of 2FA systems … Vulnerabilities in SS7 and other cellular protocols aren’t new. They have been presented at security conferences for years … there are other more secure protocols available now that systems can switch to…

Cyber security researchers began issuing warning about this flaw in late 2014 about dangerous flaws in SS7. I wrote about the SS7 flaw in September of 2016  and in March 2107. Maybe this will be the wake up call for the carriers. One industry insider quipped:

This latest attack serves as a warning to the mobile community about what is at stake if these loopholes aren’t closed … The industry at large needs to go beyond simple measures such as two-factor authentication, to protect mobile users and their data, and invest in more sophisticated mobile security.

man-in-the-middle attackIn 2014 security researchers first  demonstrated that SS7 could be exploited to track and eavesdrop on cell phones. This new attack is essentially a man-in-the-middle attack on cell phone communications. It exploits the lack of authentication in the communication protocols that run on top of SS7.

Developed in 1975, today, over 800 telecommunications companies around the world, including AT&T (T) and Verizon (VZ), use SS7 make sure their networks interoperate. This technology has not kept up with modern times.  In May 2017, Wired published an article which explains some of the ways to secure SS7. Overcoming SS7 insecurity requires implementing a series of firewalls and filters that can stop the attacks. Researchers Wired spoke to suggest that adding encryption to SS7 would shield network traffic from prying eyes and bolster authentication. Both of these changes are unpopular with the carriers, because they cost money and can impact the network core, so don’t expect any network changes to address the SS7 flaw anytime soon.

Carriers should use SS7 firewall to secure the SS7 networkThe Register reports that the FCC’s Communications Security, Reliability and Interoperability Council found that the proposed replacement for SS7 on 5G networks, dubbed the Diameter protocol has security holes too.

In March 2017, Oregon Sen. Ron Wyden and California Rep. Ted Lieu sent a letter to Homeland Security’s John Kelly requesting that DHS investigate and provide information about the impact of SS7 vulnerabilities to U.S. companies and governmental agencies. Kelly has not responded to the letter, according to the Wired article.

Of course the TLA’s would never use this “flaw” in SS7 to spy on us.

The Guardian says that given that the SS7 vulnerabilities reside on systems outside of your control, there is very little you can do to protect yourself beyond not using the services.

PoliticianThey recommend for text messages, avoiding SMS and instead using encrypted messaging services such as Apple’s (AAPL) iMessage, Facebook‘s (FB) WhatsApp or the many others available will allow you to send and receive instant messages without having to go through the SMS network to protect your messages from surveillance.

For calls, the Guardian recommends using a service that carries voice over data rather than through the voice call network. This will help prevent your calls from being snooped on. Messaging services including WhatsApp permit calls. Silent Circle’s end-to-end encrypted Phone service or the open-source Signal app also allow secure voice communications.

protect yourself Your location could be being tracked at any stage when you have your mobile phone on. The only way to avoid it is to turn off your phone or turn off its connection to the mobile phone network and rely on Wi-Fi instead.

Related articles

Ralph Bach has blogged from his Bach Seat about IT, careers and anything else that catches his attention since 2005. You can follow me at Facebook and Twitter. Email the Bach Seat here.

Your Mobile is Leaking

Your Mobile is LeakingThere is a vulnerability in the global phone system that allows hackers to get access to others’ telephone data using nothing but a phone number. The flaw is in the Signaling System 7 (PDF) or SS7 which is a set of telephony signaling protocols that exchanges information telephone networks.

listen to phone callsThe Register points out that SS7 signalling technology was developed in the 1970s and hasn’t been updated since, since the systems became accessible over the internet. The reported weakness in SS7 allows hackers or TLA’s to exploit the vulnerability with the phone number of the user they’re targeting to listen to phone calls, read text messages and track the user’s location.

A white paper (PDF) by independent cyber-security company Positive Technologies explains:

The process of placing voice calls in modern mobile networks is still based on SS7 technology which dates back to the 1970s. At that time, safety protocols involved physical security of hosts and communication channels, making it impossible to obtain access to an SS7 network through a remote unauthorised host. In the early 21st century, a set of signalling transport protocols called SIGTRAN were developed. SIGTRAN is an extension to SS7 that allows the use of IP networks to transfer messages.

However, even with these new specifications, security vulnerabilities within SS7 protocols remained. As a result, an intruder is able to send, intercept and alter SS7 messages by executing various attacks against mobile networks and their subscribers.

The real world result of the SS7 flaw as Alex Mathews, technical manager EMEA of Seoul Korea based Positive Technologies explained is:

Chat applications such as WhatsApp, Telegram, and others use SMS verification based on text messages using SS7 signalling to verify identity of users/numbers.

send SMS messages via the SS7 networkSMS authentication is one of the major security mechanisms for services like WhatsApp, Viber, Telegram, Facebook (FB), and is also part of second factor authentication for Google (GOOG) accounts, etc. Devices and applications send SMS messages via the SS7 network to verify identity, and an attacker can easily intercept these and assume identity of the legitimate user. Having done so, the attacker can read and write messages as if they are the intended recipient.

If chat history is stored on the server, this information can also be retrieved.

The hack first came to light in 2014 when security researcher Karsten Nohl demonstrated it at a convention in Germany according to FierceWireless. CBS 60 Minutes (rb- That’s still on?) caused a mild ripple after they engaged Mr. Nohl to show the vulnerability to track a new iPhone that had been given to U.S. Rep. Ted Lieu (D-CA). Mr. Lieu, who holds a degree in computer science from Stanford, agreed to use the phone to talk to his staff knowing it would be hacked. From his office in Berlin, Mr. Nohl was able to track Mr. Lieu’s movements in Los Angeles as well as to read messages and record phone calls between Representative Lieu and his staff.

U.S. cellphone networks were secureCBS correspondent Sharyn Alfonsi contacted representatives from CTIA who said that there have been reports of SS7-related security breaches abroad, “but (they) assured us that all U.S. cellphone networks were secure,” although Mr. Lieu was on a U.S. network when his phone was hacked from Germany.

The flaw “is an open secret among the world’s intelligence agencies — including ours — and they don’t necessarily want that hole plugged,” Ms. Alfonsi reported. The four major U.S. wireless operators declined to discuss more specific questions from FierceWireless. When asked whether the flaw may threaten the privacy and security of subscribers, AT&T (T) and Verizon (VZ) to CTIA, while Sprint (S) and T-Mobile (TMUS) declined to discuss SS7.

listen to phone calls,Representative Lieu has called for a congressional investigation of the vulnerabilities in SS7, writing 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 House Oversight and Government Reform Committee, of which he is a member.

The Register reports that Senator Ron Wyden (D-OR) recently joined Representative Lieu to send an open letter [PDF] to Homeland Security Secretary John Kelly asking for an update on its progress in addressing the SS7 design shortcomings. It also asks why the agency isn’t doing more to alert the public about the issue. The letter states in part:

We suspect that most Americans simply have no idea how easy it is for a relatively sophisticated adversary to track their movements, tap their calls, and hack their smartphones,” “We are also concerned that the government has not adequately considered the counterintelligence threat posed by SS7-enabled surveillance.


It is important to understand that the wired and wireless telephone network that your phone connects to is not secure and probably never will be.

Telephone networks were not designed to be secure.

In the most recent draft of the new Digital Identity Guidelines requirements from NIST warns that:

Note: Out-of-band authentication using the PSTN (SMS or voice) is discouraged and is being considered for removal in future editions of this guideline.

You really have to wonder if this is related to the SS7 hole and why it is only being considered for removal. Maybe some of its TLA friends want the hole to stay in place.

I previously covered the SS7 flaw implications to SMS here.


Ralph Bach has blogged from his Bach Seat about IT, careers and anything else that catches his attention since 2005. You can follow me at Facebook and Twitter. Email the Bach Seat here.

SMS is Done

SMS is DoneFollowers of the Bach Seat know that passwords suck and no longer provide reliable security. Because automated mass cybercrime attacks are hammering businesses daily, the National Institute of Standards and Technology (NIST) is disrupting the online security status–quo. According to InfoWorld the US government’s standards body has decided that passwords are not good enough anymore. NIST now wants government agencies to use two-factor authentication (2FA) to secure applications, networks, and systems. Two factor authentication is a security process where the user provides two means of identification from separate categories of credentials. The first is typically something you have, a physical token, such as a card. The second is usually something you know like a PIN number.

National Institute of Standards and Technology (NIST)The proposed standard discourages organizations from sending special codes via SMS messages. Many services offer two-factor authentication. They ask users to enter a one-time passcodes sent via SMS into the app or site to verify the transaction. The author writes that weaknesses in the SMS mechanism concerns NIST.

NIST now recommends that developers use tokens and software cryptographic authenticators instead of SMS to deliver special codes. They wrote in a draft version of the DAG; “OOB [out of band] using SMS is deprecated and will no longer be allowed in future releases of this guidance.”

Short Message Service (SMS)Federal agencies must use applications that conform to NIST guidelines. This means for software to be sold to federal agencies, it must follow NIST guidelines. InfoWorld says this is especially relevant for secure electronic communications.

SMS-based 2FA is considered insecure by NIST for a number of reasons. First, someone other than the user may be in possession of the phone. The author says an attacker with a stolen phone would be able to trigger the login request. In some cases, the contents of the text message appear on the lock screen, which means the code is exposed to anyone who glances at the screen.

SMS based two-factor authentication (2FA)InfoWorld says that NIST isn’t deprecating SMS-based methods simply because someone may be able to intercept the codes by taking control of the handset, that risk also exists with tokens and software authenticators. The main reason NIST appears to be down on SMS is because it is insecure over VoIP.

The author says there has been a significant increase in attacks targeting SMS-based two-factor authentication recently. SMS messages can be hijacked over some VoIP services. SMS messages delivered through VoIP are only as secure as the websites and systems of the VoIP provider. If an attacker can hack the VoIP servers or network they can intercept the SMS security codes or have them rerouted to her own phone. Security researchers have used weaknesses in the SMS protocol to remotely interact with applications on the target phone and compromise users.

Signalling System 7 (SS7) Sophos’ Naked Security Blog further explains some of the risks. There is malware that can redirect text messages. There are attacks against the This hack

Mobile phone number portability also poses a problem for SMS security. Sophos says that phone ports, also known as SIM swaps can make SMS insecure. SIM swap attacks are where an attackers convinces your mobile provider issues you a new SIM card to replace one that’s been lost, damaged, stolen or that is the wrong size for your new phone.

SIM swap attacksSophos also says in many places it is very easy for criminals to convince a mobile phone store to transfer someone’s phone number to a new SIM and therefore hijacking all their text messages.

ComputerWorld highlights a recent attack used social engineering to bypass Google’s two-factor authentication. Criminals sent users text messages informing them that someone was trying to break into their Gmail accounts and that they should enter the passcode to temporarily lock the account. The passcode, which was a real code generated by Google when the attackers tried to log in, arrived in a separate text message, and users who didn’t realize the first message was not legitimate would pass the unique code on to the criminals.

Password“NIST’s decision to deprecate SMS two-factor authentication is a smart one,” said Keith Graham, CTO of authentication provider SecureAuth. “The days of vanilla two-factor approaches are no longer enough for security.”

For now, applications and services using SMS-based authentication can continue to do so as long as it isn’t a service that virtualizes phone numbers. Developers and application owners should explore other options, including dedicated two-factor apps. One example is Google Authenticator, which uses a secret key and time to generate a unique code locally on the device for the user to enter into the application.

Hardware tokens Hardware tokens such as RSA’s SecurID display a new code every few seconds. A hardware security dongle such as YubiKey, used by many companies including Google and GitHub, supports one-time passwords, public key encryption, and authentication. Knowing that NIST is not very happy with SMS will push the authentication industry towards more secure options.

Many popular services and applications offer only SMS-based authentication, including Twitter and online banking services from major banks. Once the NIST guidelines are final, these services will have to make some changes.

fingerprint recognitionMany developers are increasingly looking at fingerprint recognition. ComputerWorld says this is because the latest mobile devices have fingerprint sensors. Organizations can also use adaptive authentication techniques, such as layering device recognition, geo-location, login history, or even behavioral biometrics to continually verify the true identity of the user, SecureAuth’s Graham said.

NIST acknowledged that biometrics is becoming more widespread as a method for authentication, but refrained from issuing a full recommendation. The recommendation was withheld because biometrics aren’t considered secret and can be obtained and forged by attackers through various methods.

Biometric methods are acceptable only when used with another authentication factor, according to the draft guidelines. NIST wrote in the DAG;

Biometrics[Biometrics] can be obtained online or by taking a picture of someone with a camera phone (e.g. facial images) with or without their knowledge, lifted from objects someone touches (e.g., latent fingerprints), or captured with high-resolution images (e.g., iris patterns for blue eyes)

At this point, it appears NIST is moving away from recommending SMS-based authentication as a secure method for out-of-band verification. They are soliciting feedback from partners and NIST stakeholders on the new standard. They told InfoWorld, “It only seemed appropriate for us to engage where so much of our community already congregates and collaborates.”

You can review the draft of Special Publication 800-63-3: Digital Authentication Guidelines on Github or on NIST’s website until Sept. 17. Sophos recommends security researcher Jim Fenton’s presentation from the PasswordsCon event in Las Vegas that sums up the changes.

VentureBeat offers some suggestions to replace your SMS system:

  • Hardware tokens that generate time-based codes.
  • Apps that generate time-based codes, such as the Google Authenticator app or RSA SecurID,
  • Hardware dongles based on the U2F standard.
  • Systems that use push notifications to your phone.


Ralph Bach has blogged from his Bach Seat about IT, careers and anything else that catches his attention since 2005. You can follow me at Facebook and Twitter. Email the Bach Seat here.