A previously undiscovered flaw in the WhatsApp messaging application allowed an attacker to target human rights activists and lawyers by compromising mobile phones and installing commercial-grade spyware just by making a call, Facebook and independent researchers stated on Tuesday.
A variety of government agencies, security companies, and digital rights activists warned WhatsApps users of the seriousness of the issue, although users have been protected since the Facebook subsidiary blocked the attack vector on the network late last week, the company said in a statement. WhatsApp briefed several human rights organizations on the attack over the past few days.
"We believe a select number of users were targeted through this vulnerability by an advanced cyber actor," the company said. "The attack has all the hallmarks of a private company reportedly that works with governments to deliver spyware that takes over the functions of mobile phone operating systems."
The attack shows the dangers of zero-day vulnerabilities, which are often sold to private companies and government agencies. The current exploit appears to be part of a spyware program called Pegasus, developed by Israeli cyber-offense firm NSO Group and sold to governments for surveillance purposes. The NSO Group, and other offensive tool providers, incorporate exploits for undiscovered security issues into their attack tools to give their customers the ability to hack into the technology used by targeted citizens and companies.
The University of Toronto's Citizen Lab, a digital-rights research group, warned that evidence suggests that a human-rights lawyer was targeted by the attack over the weekend. On May 14, both the UK National Cyber Security Centre and the US Cybersecurity and Infrastructure Security Agency warned users to upgrade to the latest version of WhatsApp.
"This new type of attack is deeply worrying and shows how even the most trusted mobile apps and platforms can be vulnerable," Mike Campin, vice president of engineering for security firm Wandera, said in a statement. "While this attack is based on a previously identified exploit known as Pegasus, the fact that it has been repackaged into a form that can be delivered via a simple WhatsApp call has shocked many."
WhatsApp is considered to be a fairly secure, yet easy to use, messaging application, and so many activists, journalists, and dissidents use the application to protect their communications. It is relatively unclear how many people were targeted with the latest attack.
The Financial Times, which broke the story on May 13, noted that WhatsApp has been targeted successfully in the past with attacks that allowed specially crafted text messages to force affected phones to download the attacker's spyware. WhatsApp has not yet estimated the number of people affected.
By all accounts, WhatsApp acted quickly and blunted the impact of the attack, but parent company Facebook gave very few details of the vulnerability or what happened. A vulnerability report published by the company on May 13 consisted of two sentences:
"A buffer overflow vulnerability in WhatsApp VOIP stack allowed remote code execution via specially crafted series of SRTCP packets sent to a target phone number," the company stated, adding a second line listing the affected versions.
WhatsApp uses the secure real-time transport protocol, or SRTCP, to establish connections between clients and allow for audio and video calls. In this case, the code used to handle incoming data had a buffer overflow vulnerability, says John Kozyrakis, staff research engineer at Synopsys.
"Buffer overflow bugs are very common in code that parses incoming packets of complicated protocols due to the large attack surface," he says, adding that by crafting a series of malicious SRTCP packets and sending them to a client identified by a phone number, an attacker could exploit the vulnerability. "The client is going to process this malicious packets and due to the buffer overflow bug, it will allow the attacker to also execute arbitrary code on the user’s device."
An analysis by network security firm Checkpoint Software Technologies gives more details of the attack and how Facebook patched the WhatsApp application.
Despite the attack, security professionals continue to describe WhatsApp as a secure messaging application.
"WhatsApp remains one of the most safe and secure messaging clients, as far as security features are concerned, like encryption, message authentication, integrity, (and) replay protection," Kozyrakis says. "[Another messaging app called Signal] uses the ZRTP protocol instead of SRTCP and may be considered more safe, while other messenger apps less so."
WhatsApp's quick response has likely cost the attackers, Bob Rudis, chief data scientist at vulnerability management firm Rapid7, said in a statement.
"This means they 'burned' the exploit—that is, wasted a valuable exploit on a campaign—since it's now widely known and will get lots of attention and be patched by users pretty quickly," he said. "These exploits tend to not be cheap so unless they really did get to their intended victims and find whatever they were looking for, this was a potentially big fail on their part."