![]() When you buy through links on our site, we may earn an affiliate commission. for initial provisioning), and disable it again afterwards–in order to avoid any such forms of exploitation.Yoodley is reader-supported. We are also investigating how to have a configuration option: how to opt-in to SAT, if you really need it (e.g. Purism is actively working with its modem manufacturers in order to protect Librem 5 users from such exploits. The mobile then sends it back to the attacker, exposing for example what the user cell tower ID is. It is not visible to the user and will initiate, again without the user knowing, an automated response by the mobile. This is possible when attackers send a specially crafted SMS to a mobile. And it must be assumed that more information about the user can very well be extracted in a similar way. An attacker would thus be able to locate a user–accurately enough to determine, for example, if someone is at home or not. The cell tower ID can easily be matched against databases, and is pretty much equal to having a geographical position. It allows for exposing critical user data, like the currently connected cell tower ID. One of these flaws has just surfaced: it is called SIM Jacker, and it exploits the Browser component, found in many SIM cards. Their code is not public, and is thus likely to contain security flaws. ![]() But their implementation details are not public. SAT applets are an important part of the provisioning by the operators, when new SIM cards get activated. SAT applets can also interact with the user, if the handset implements the user interface parts of SAT with simple menus, limited icon display and reading input from the ‘dial pad’. sending SMS) and can get updated and/or changed by the operator, over the air. SAT applets can even initiate unsolicited communication (e.g. They can execute on the SIM card–pretty much without any knowledge from the user. SAT applets can have access to modem traffic, especially to SMS. The SAT defines a standard way to interface the SAT applets with the modem and the phone. Most are based on the JavaCard standard and can be programmed with small Java applets. They are small computers on their own, they run code, and they can indeed be programmed. The name SAT tells us not only that it is SIM-related, but also that it contains the term application: SIM cards can, and today they usually do, indeed contain small applications or applets. It was to make this (and other things) as convenient and least painful as possible for users that SAT was invented. The process for this initial setup is (also) called provisioning. To make this even more complicated, these details (and the way to set them up) are different from operator to operator. ![]() All this needs to be properly set up in the mobile, to make full use of both the mobile and the network. And setting up these cards has become more and more complicated you need an SMS center number, details for the MMS server, mailbox dial-in number… and a lot more. This data set grants you access to the operator’s network.īut phones have become more and more powerful. The SIM card used to be a fairly simple device, which you can imagine as the key to unlock the access to the network: i.e., it stores a secret (a cryptographic key) along with an ID (the IMSI) and some details about the issuing operator, etc. ![]() It is the tiny chip card you insert into your phone, to get access to the cellular network of an operator. Its name already points to the origin: the SIM card. The same is true for something that many mobile phone users are totally unaware of–the SIM Application Toolkit, also called SIM Toolkit, SAT/USAT or STK. It is a piece of software, software has bugs and so has the ME implementation the news are full of it lately. It is even undocumented in most parts, so it can not be publicly reviewed and audited. ![]() The ME, for example, is fully proprietary and closed. Sadly, many of these technologies that were meant as good are implemented in a way that bears more harm than advantages. And if you have to manage a large fleet of machines, distributed within a larger enterprise, this can save huge amounts of effort, time–and thus money. It allowed for remote access on a very low level, so they could even do complete remote reinstalls of a machine. The Management Engine in Intel’s CPUs, for instance, was intended to make the life of admins easier. Technologies are often created with good intent, to make our life easier, to solve problems in a convenient way. Librem 14: Adding Librem EC, Freed Embedded Controller Firmware - February 22, 2021.Unleashing the Librem 14 - July 6, 2022. ![]()
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