Pierluigi Paganini August 31, 2016

Its name is the Trident: a chain of zero-day exploits that aim to infect iPhone with commercial spyware. Researchers linked it to the NSO group.

Its name is the Trident: a chain of zero-day exploits that aim to infect iPhone with commercial spyware.
Researchers say it’s belonging to an exploit infrastructure connected to the NSO group.

Image from lookout.com

Thanks to the great work made by the researchers from the Citizenlab organization and the Lookout firm that responsibly disclosed the exploits and their related vulnerabilities to Apple.
Given the severity of the Trident, Apple worked extremely quickly to patch these vulnerabilities and it has released iOS 9.3.5 to address them.

In this post, we want to give you a description and some technical information about the inner logic of the Trident exploit instead of the attack received by Ahmed Mansoor.
With the episode of Ahmed Mansoor we can quickly understand the infection vector of that exploit: SMS, email, social media, or any other message.

The most scaring part of that attack is that the single action the user have to do to trigger this dangerous attack is just a click on an external link.
The exploit seems to contain the logic to remote jailbreak an iPhone to install arbitrary applications and then deliver a commercial spyware called Pegasus as an espionage software to track the victim.

What is Pegasus and who is behind it?

Pegasus  is a spy software installable on iOS devices that allow reading messages, emails, passwords and address lists as well as eavesdropping on phone calls, making and transmitting audio recordings and tracking the location on a compromised device (but we will look better in the following section).
It seems that this spyware is attributed to NSO Group, an Israeli firm based in Herzliya in the country’s “Silicon Valley”.

This spyware was attributed to the NSO Group because in the Mansoor’s attack the domain used for the phishing message (webdav.co) belongs to a network of domains that is a part of an exploit infrastructure provided by the company NSO Group.

NSO Group, now owned by US private equity firm Francisco Partners Management, has flown far under the radar, without even a website.

The Citizenlab reported that just opening the link included in the message sent to the victims with an iPhone version 9.3.3 it is possible to observe an active unknown software that was remotely implanted into the system through the delivery of unknown exploits from that link.
The complex exploit takes the name as Trident.

ATTACK SCENARIO
After the user get baited the exploit start his work to infect the phone, following the 3 main stages of that attack, better detailed here:

1. Delivery and WebKit vulnerability

This stage comes down over the initial URL in the form of an HTML file that exploits a vulnerability (CVE-2016-4655) in WebKit (used in Safari and other browsers).
CVE-2016-4655: Memory Corruption in Safari WebKit
A memory corruption vulnerability exists in Safari WebKit that allows an attacker to execute arbitrary code. Pegasus exploits this vulnerability to obtain initial code execution privileges within the context of the Safari web browser.

2. Jailbreak

This stage is downloaded from the first stage code based on the device type (32-bit vs 64- bit). Stage 2 is downloaded as an obfuscated and encrypted package. Each package is encrypted with unique keys at each download, making traditional network-based controls ineffective. It contains the code that is needed to exploit the iOS Kernel (CVE-2016-4656 and CVE-2016-4657) and a loader that downloads and decrypts a package for stage 3.

CVE-2016-4656: Kernel Information Leak Circumvents KASLR
Before Pegasus can execute its jailbreak, it must determine where the kernel is located in memory. Kernel Address Space Layout Randomization (KASLR) makes this task difficult by mapping the kernel into different and unpredictable locations in memory. In short, before attacking the kernel, Pegasus has to find it. The attacker has found a way to locate the kernel by using a function call that leaks a non-obfuscated kernel memory address in the return value, allowing the kernel’s actual memory location to be mapped.
CVE-2016-4657: Memory Corruption in Kernel leads to Jailbreak
The third vulnerability in Pegasus’ Trident is the one that is used to jailbreak the phone. A memory corruption vulnerability in the kernel is used to corrupt memory in both the 32- and 64-bit versions. The exploits are performed differently on each version.

3. Espionage software:
   This stage is downloaded by stage 2 and is also based on the device type (32-bit vs 64-bit). Stage 3 contains the espionage software, daemons, and other processes that are used after the device has been jailbroken in stage 2. Stage 3 installs the hooks into the applications the attacker wishes to spy on. Additionally, stage 3 detects if the device was previously jailbroken through another method and, if so, removes any access to the device that the jailbreak provides, such as via SSH. The software also contains a failsafe to remove itself if certain conditions are present.

Jailbreak Persistence

Once the kernel has been exploited, both exploits perform similar tasks to prepare the system to be jailbroken:
• Disable kernel security protections including code signing
• Remount the system partition
• Clear the Safari caches (to help cover their tracks)
• Write the jailbreak files (including the main loader as /sbin/mount_nfs)
As a final step of stage 2, the exploit removes /etc/nfs.conf which triggers the file to load /sbin/mount_nfs (which is the stage 3 jailbreakloader). Because /sbin/mount_nfs is run as root, the code is run with full privileges. After stage 3 will be unpacked, Pegasus need to gain persistence on device reboot. So exploit replaces the system daemon rtbuddyd with a copy of the jsc binary and creates a link to a script that is similar to the exploit for CVE-2016-4655 .

THE ESPIONAGE SOFTWARE

“Pegasus is one of the most sophisticated pieces of surveillance and espionage software” stated Lookout company. It has a novel mechanism to install and hide itself and obtain persistence on the system. Once it is resident, it uses a number of ways to hide its communications and protect itself from discovery, and it hooks into a large number of the phone’s functions in order to gather data and intercept messages and calls.

Following we will list all the features Pegasus have to spy on the victim a fully detailed list with references of source code):

• Persistence: JSC Privilege Escalation
• Disabling Updates
• Jailbreak Detection
• Device Monitoring (Current Reachability, Sim and cell network information, Call info, SIM/Network change notification)
• Stealth Update to Command & Control Infrastructure
• Self Destruction
• Steal Calendar
• Steal Contacts
• Steal GPS location
• Capturing User Passwords
• WiFi and Router Passwords
• Interception of Calls and Messages

Following an image of an infected phone by Pegasus compared to a normal one:

Image from lookup.com

CONCLUSION

NSO Group reportedly has hundreds of employees and makes millions of dollars in annual revenue, effectively as a cyber arms dealer, from the sale of its sophisticated mobile attack software.

We strongly recommend to all iPhone owners to update to the latest version of iOS (9.3.5) immediately.

REFERENCES:

• https://info.lookout.com/rs/051-ESQ-475/images/lookout-pegasus-technical-analysis.pdf
• https://citizenlab.org/2016/08/million-dollar-dissident-iphone-zero-day-nso-group-uae/
• http://www.securityweek.com/iphone-spyware-spotlights-israels-secretive-surveillance-industry

Written by the IT Security Expert Antonio Cocomazzi

Antonio Cocomazzi is an IT Security Expert specialized in the malware analysis field. Young and recently graduated, he conducts a 6 months research focused on Ransomware giving a full characterization of the recent families defining a new methodology for dissecting this kind of malware.

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Pierluigi Paganini

(Security Affairs – Trident exploit, iPhone)