T-Mobile MITM, a starting point to discuss mobile security

Pierluigi Paganini March 23, 2013

Many times we discussed about large diffusion of mobile devices and of related cyber threats, around a months ago I presented the case of HTC mobile that revealed 18 million devices commercialized by Taiwanese company had security flaws that could exposes users to serious risks, in particular the bugs could allow the theft of information stored on the mobile and the tracking of user’s location.

This time a default “Wi-Fi Calling” feature implemented  in some of T-Mobile devices is the cause of much concern because it lets Android users vulnerable to Man-in-the-Middle attack. The feature, discovered by Jethro Beekman and Christopher Thompson students at University of California Berkeley, keeps mobiles of T-Mobile company (a division of Deutsche Telekom) connected in area with little or no coverage using Wi-Fi connection.

The researchers reverse-engineered the Wi-Fi Calling feature, which is based on a standard voice-over-IP (VoIP) protocol over an encrypted connection.

The ideal condition to perform a Man In The Middle attack is to share the same network segment with victim, in the case of wireless network the simplest scenarios is represented by an open network.


In the above picture P) is the mobile Phone,  (AP) the Access point and (M) the illegitimate Man-in-the-middle that trick users before to transfer info to (S) Service provider.

If the attackers have knowledge of network parameters and configuration they can use an ‘Evil Twin’ attack, it consists to setup a network that imitates the legitimate one and tricks users into connecting to that rogue network instead, by showing up in the list of available Wi-Fi networks.

An attacker could exploit the feature to gather access to victims mobile modifying calls and messages on certain Android smartphones.

The mutual authentication between mobiles and T-mobile server is part of a PKI infrastructure,  but it leak of a proper validation process that allow attacker to create a fake certificate that could be used to set-up an illegitimate server that pretend to be the T-Mobile server.

“The certificate chain returned by T-Mobile’s server is shown in Figure 2. Two things stand out: first, the common name of the first certificate is simply the IP address of the server; second, the self-signed root certificate is not included in standard Certificate Authority (CA) distributions. In fact, searching the webfor the exact common name of the root yielded barely any results. This can meant that the root certificate was either built-in to T-Mobile’s client software, or they did not implement certificate validation correctly.In fact, the client does not seem to have any problems with sslsniff intercepting the connection, making us conclude the latter. Analysis of the binaries confirmed that there was no trace of the root certificate.” The research paper reported.


“Without this proper verification, hackers could have created a fake certificate and pretend to be the T-Mobile server,” “This would have allowed attackers to listen to and modify traffic between a phone and the server, letting them intercept and decrypt voice calls and text messages sent over Wi-Fi Calling.” explained the researchers.

The students Beekman and Thompson informed T-Mobile of the problems last December and  on few days ago, on March 18th the company issued a patch to fix the problem.

What is very concerning is that this kind of vulnerabilities could potentially affect millions of mobile users, other telephone carriers in the world, such as Rogers Wireless in Canada and Orange in Britain,  suffer similar problems due the implementation of unsecure features.

Last October, Beekman and Thompson published a study that revealed that many applications failed to properly implement SSL exposing users to basic Man-In-The-Middle attacks. On 13,500 of the most popular free applications on Google Play at the time, 8% implemented a vulnerable SSL and some of them collected a substantial amount of personal information.

The situation is very concerning … let me conclude with a phrase that should give us pause

“In wireless networks, an attacker no longer needs physical access to invade a network. “

The mobile technology is growing and security must be an essential requirement since design phase!

Pierluigi Paganini

(Security Affairs – Mobile)

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