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Israeli surveillance company NSO Group has reportedly utilized a series of zero-day exploits, including a previously unknown one named "Erised," targeting WhatsApp vulnerabilities to deploy its Pegasus spyware via zero-click attacks, despite facing legal action.

Pegasus is NSO Group's spyware platform, marketed as surveillance software for governments globally. It includes various components that allow clients to thoroughly monitor and extract information from the compromised devices of their targets. With the Pegasus agent on a victim's mobile device, NSO customers could easily monitor user activity.

Court documents filed on Thursday, highlighted by Citizen Lab senior researcher John Scott Railton, are part of WhatsApp's ongoing legal battle with NSO Group. These documents reveal that the company had created an exploit called ‘Heaven’ before April 2018. This exploit used a custom WhatsApp client known as the ‘WhatsApp Installation Server’ (WIS), enabling it to impersonate official clients and deploy Pegasus from a third-party server controlled by NSO.

WhatsApp managed to block NSO's access to infected devices and control servers by releasing security updates in September and December 2018, effectively neutralizing the Heaven exploit.

By February 2019, NSO reportedly developed another exploit named 'Eden' to overcome the security measures WhatsApp established in 2018. In May 2019, WhatsApp discovered that Eden was employed by NSO clients in attacks on around 1,400 devices.

Court documents reveal, "NSO admits to developing and selling the spyware outlined in the Complaint, specifically the zero-click installation vector called 'Eden.' This was part of the WhatsApp-based vector family known as 'Hummingbird,' responsible for the attacks."

Tamir Gazneli, NSO's head of research and development, alongside other defendants, confessed to creating these exploits by decompiling and reverse-engineering WhatsApp's code. This led to the development of the WIS client, which sent malformed messages through WhatsApp servers to install the Pegasus agent, breaching both federal and state laws and violating WhatsApp's Terms of Service.

Upon discovering these attacks, WhatsApp patched the Eden vulnerabilities and disabled NSO's accounts. Despite the Eden exploit being blocked in May 2019, court documents state NSO admitted to creating another installation vector named 'Erised,' which manipulated WhatsApp's relay servers to deploy Pegasus spyware.

These documents further detail that NSO continued to use and offer Erised to their clients even after they were sued in October 2019, until WhatsApp implemented further changes that blocked access beyond May 2020. NSO witnesses reportedly declined to answer if the company devised additional WhatsApp-based malware vectors.

The spyware vendor confessed in court to using WhatsApp’s service to install Pegasus on "between hundreds and tens of thousands" of devices. It also admitted to reverse-engineering WhatsApp to develop the capability, installing the technology for clients and providing necessary WhatsApp accounts for the attacks.

The spyware installation was initiated when a Pegasus client entered a target's phone number into their laptop software, leading to Pegasus being deployed on the victim's device remotely. This process required no technical expertise from the client, as they only needed to input the target number and select "Install," with NSO's system taking care of the rest.

NSO maintains that they are not liable for customer actions and claim no access to the data obtained during the Pegasus spyware installations, thereby limiting their involvement in surveillance activities.

NSO's Pegasus spyware was reportedly used to compromise the phones of Catalan politicians, journalists, activists, United Kingdom government officials, Finnish diplomats, and U.S. Department of State employees.

In November 2021, the United States imposed sanctions on NSO Group and Candiru for supplying software used for surveillance of government officials, journalists, and activists. That same month, Apple filed a lawsuit against NSO for hacking into iOS devices and spying on users with Pegasus.

A spokesperson for NSO Group was unavailable for comment when contacted by BleepingComputer earlier today.