The latest update released by Silent Circle for its privacy-focused Blackphone 1 patches several security flaws, including a modem vulnerability that could have been exploited by malicious actors to take control of the device.
Blackphone, considered one of the most secure smartphones, is shipped with applications designed to encrypt voice and text communications in an effort to prevent unauthorized parties from intercepting potentially sensitive information.
While preparing a reverse engineering exercise for a training session, researchers at endpoint security firm SentinelOne discovered that the Blackphone had an open and accessible socket. After doing some further digging, experts discovered that the socket was associated with NVIDIA’s Icera modems. NVIDIA acquired Icera in 2011 as part of its plans to enter the smartphone market, but the tech giant decided to abandon Icera modems in May 2015.
An analysis revealed that an Icera modem binary named agps_daemon interacted with the open socket. Agps_daemon, which had elevated privileges, listened on the open socket and wrote anything it received to a port that it opened (ttySHM3).
Experts determined that this could be used to communicate with the device’s modem since it listened to the ttySHM3 port.
According to SentinelOne, an attacker with shell user privileges could have exploited this flaw to send commands to the modem. An attacker could have also created a special Android application, one with Internet permissions, to send the commands.
The list of commands available to an attacker includes ones for muting the modem to prevent ringing, toggling caller ID on outgoing calls, sending and receiving SMS messages without the victim’s knowledge, setting up call forwarding and preventing the user from seeing the incoming call, connecting a call (visible to the victim), silently checking the state of phone calls, resetting various settings, forcing conference calls, and finding neighboring cell towers.
Tim Strazzere, director of mobile research at SentinelOne, told SecurityWeek that an attacker would need to find a way to execute code on the targeted device before exploiting this vulnerability. This could be done using malware disguised as an application that the user is tricked into installing on their Blackphone.
“An example of a chained attack might be using a remote code execution bug found somewhere else on the system, then leveraging this attack to control the radio to do something like intercept SMS,” Strazzere explained.
Based on what an attacker can accomplish by exploiting this vulnerability, Strazzere said he would rate the issue as having medium-high severity.
This vulnerability, which Silent Circle has classified as a potential privilege escalation (CVE-2015-6841), was reported by SentinelOne via BugCrowd in late August. The standard reward offered by Silent Circle as part of its BugCrowd-hosted bug bounty program is $128 per bug, but in this case SentinelOne was awarded $500.
The vulnerability was patched by Silent Circle on Dec. 7 with the release of PrivatOS 1.1.13 RC3, which also resolves several other security holes, including denial-of-service (DoS), information disclosure, privilege escalation, code execution and Stagefright flaws.
Silent Circle has clarified in a blog post that the vulnerability affects Blackphone 1 running versions 1.1.13 RC2 and prior of PrivatOS, but Blackphone 2 is not impacted. The vendor says it’s safe to assume that the vulnerability affects any device using the NVIDIA Icera modem.
By default, the Blackphone is designed to periodically check for PrivatOS updates, which are installed over-the-air (OTA).
While Silent Circle's Blackphone has enjoyed the spotlight as a top smartphone catering to security and privacy minded individuals, Silicon Valley-based Macate today unveiled the new security-focused "GATCA Elite cyberphone", which combines advanced security and encryption features. Unveiled at the CES tradeshow in Las Vegas, the Android-based device comes with security modules such as intelligent human authentication, advanced encryption to prevent hacking and spoofing, dual SIM cards, and a suite of pre-loaded software and apps.
*Updated to clarify that the vulnerability only affects Blackphone 1; Blackphone 2 is not impacted
Related: Silent Circle Ships Blackphone 2