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Easy SMS Hijacking

Vice is reporting on a cell phone vulnerability caused by commercial SMS services. One of the things these services permit is text message forwarding. It turns out that with a little bit of anonymous money — in this case, $16 off an anonymous prepaid credit card — and a few lies, you can forward the text messages from any phone to any other phone.

For businesses, sending text messages to hundreds, thousands, or perhaps millions of customers can be a laborious task. Sakari streamlines that process by letting business customers import their own number. A wide ecosystem of these companies exist, each advertising their own ability to run text messaging for other businesses. Some firms say they only allow customers to reroute messages for business landlines or VoIP phones, while others allow mobile numbers too.

Sakari offers a free trial to anyone wishing to see what the company’s dashboard looks like. The cheapest plan, which allows customers to add a phone number they want to send and receive texts as, is where the $16 goes. Lucky225 provided Motherboard with screenshots of Sakari’s interface, which show a red “+” symbol where users can add a number.

While adding a number, Sakari provides the Letter of Authorization for the user to sign. Sakari’s LOA says that the user should not conduct any unlawful, harassing, or inappropriate behaviour with the text messaging service and phone number.

But as Lucky225 showed, a user can just sign up with someone else’s number and receive their text messages instead.

This is much easier than SMS hijacking, and causes the same security vulnerabilities. Too many networks use SMS as an authentication mechanism.

Once the hacker is able to reroute a target’s text messages, it can then be trivial to hack into other accounts associated with that phone number. In this case, the hacker sent login requests to Bumble, WhatsApp, and Postmates, and easily accessed the accounts.

Don’t focus too much on the particular company in this article.

But Sakari is only one company. And there are plenty of others available in this overlooked industry.

Tuketu said that after one provider cut-off their access, “it took us two minutes to find another.”

Slashdot thread. And Cory Doctorow’s comments.

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Eavesdropping on SMS Messages inside Telco Networks

Fireeye reports on a Chinese-sponsored espionage effort to eavesdrop on text messages:

FireEye Mandiant recently discovered a new malware family used by APT41 (a Chinese APT group) that is designed to monitor and save SMS traffic from specific phone numbers, IMSI numbers and keywords for subsequent theft. Named MESSAGETAP, the tool was deployed by APT41 in a telecommunications network provider in support of Chinese espionage efforts. APT41’s operations have included state-sponsored cyber espionage missions as well as financially-motivated intrusions. These operations have spanned from as early as 2012 to the present day. For an overview of APT41, see our August 2019 blog post or our full published report.

Yet another example that demonstrates why end-to-end message encryption is so important.

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Perverse Vulnerability from Interaction between 2-Factor Authentication and iOS AutoFill

Apple is rolling out an iOS security usability feature called Security code AutoFill. The basic idea is that the OS scans incoming SMS messages for security codes and suggests them in AutoFill, so that people can use them without having to memorize or type them.

Sounds like a really good idea, but Andreas Gutmann points out an application where this could become a vulnerability: when authenticating transactions:

Transaction authentication, as opposed to user authentication, is used to attest the correctness of the intention of an action rather than just the identity of a user. It is most widely known from online banking, where it is an essential tool to defend against sophisticated attacks. For example, an adversary can try to trick a victim into transferring money to a different account than the one intended. To achieve this the adversary might use social engineering techniques such as phishing and vishing and/or tools such as Man-in-the-Browser malware.

Transaction authentication is used to defend against these adversaries. Different methods exist but in the one of relevance here — which is among the most common methods currently used — the bank will summarise the salient information of any transaction request, augment this summary with a TAN tailored to that information, and send this data to the registered phone number via SMS. The user, or bank customer in this case, should verify the summary and, if this summary matches with his or her intentions, copy the TAN from the SMS message into the webpage.

This new iOS feature creates problems for the use of SMS in transaction authentication. Applied to 2FA, the user would no longer need to open and read the SMS from which the code has already been conveniently extracted and presented. Unless this feature can reliably distinguish between OTPs in 2FA and TANs in transaction authentication, we can expect that users will also have their TANs extracted and presented without context of the salient information, e.g. amount and destination of the transaction. Yet, precisely the verification of this salient information is essential for security. Examples of where this scenario could apply include a Man-in-the-Middle attack on the user accessing online banking from their mobile browser, or where a malicious website or app on the user’s phone accesses the bank’s legitimate online banking service.

This is an interesting interaction between two security systems. Security code AutoFill eliminates the need for the user to view the SMS or memorize the one-time code. Transaction authentication assumes the user read and approved the additional information in the SMS message before using the one-time code.

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NIST is No Longer Recommending Two-Factor Authentication Using SMS

NIST is no longer recommending two-factor authentication systems that use SMS, because of their many insecurities. In the latest draft of its Digital Authentication Guideline, there’s the line:

[Out of band verification] using SMS is deprecated, and will no longer be allowed in future releases of this guidance.

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