Simjacker Exploits S@T Browser to Affect a Billion Users

Platform agnostic attack, Simjacker allows hackers to remotely exploit the victims' phone by sending a SMS which contains a malicious code; the code gives instructions to the universal integrated circuit card (UICC)/ SIM card placed inside the targeted device to retrieve and carry out sensitive commands.

The attack is set into motion as soon as the 'attack SMS' sent via another remote handset, is received by the targeted device. The process involves a series of SIM Toolkit (STK) directions particularly configured to be sent on to the SIM Card inside the victim's device.

To ensure a proper execution of these instructions, Simjacker exploits the S@T Browser, which is a software found in SIM cards. After receiving the 'attack SMS', SIM card resorts to the S@T Browser library for setting up the execution friendly environment which can trigger logic on the infected device.

S@T Browser, a legacy browser technology placed inside the SIM cards on a number of handsets, was typically used to send promotional messages or spam text messages. However, the attackers went on exploiting it for obtaining device's location and its unique International Mobile Equipment Identity (IMEI).

The attacker sends a SMS to the S@T browser asking it for the aforementioned information which it would obtain and store on to the SIM card. Then, the attacker would send another SMS to acquire the stored information. These messages are send and received in binary codes, unlike regular messages. It doesn't alert the victim in any manner and hence qualifies to be a highly effective tool for attacking mobile phones via messages.

Referencing from the findings of mobile carrier security company AdaptiveMobile Security, 

"The main Simjacker attack involves an SMS containing a specific type of spyware-like code being sent to a mobile phone, which then instructs the SIM Card within the phone to ‘take over’ the mobile phone to retrieve and perform sensitive commands." 

"We believe this vulnerability has been exploited for at least the last two years by a highly sophisticated attacker group." 

The report reads. 

Notably, the exploit is working as a lot of operators are failing to check the origin of these binary codes (SMS), which can be blocked by configuring the firewall technology in their corresponding networks, advises AdaptiveMobile.

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