Hackers were able to remotely install surveillance software on phones and other devices using a major vulnerability in messaging app WhatsApp, it has been confirmed.
WhatsApp, which is owned by Facebook, said the attack targeted a “select number” of users, and was orchestrated by “an advanced cyber actor”.
A fix was rolled out on Friday.
The attack was developed by Israeli security firm NSO Group, according to a report in the Financial Times.
On Monday, WhatsApp urged all of its 1.5 billion users to update their apps as an added precaution.
The attack was first discovered earlier this month.
WhatsApp promotes itself as a “secure” communications app because messages are end-to-end encrypted, meaning they should only be displayed in a legible form on the sender or recipient’s device.
However, the surveillance software would have let an attacker read the messages on the target’s device.
“Journalists, lawyers, activists and human rights defenders” are most likely to have been targeted, said Ahmed Zidan from the non-profit Committee to Protect Journalists.
It involved attackers using WhatsApp’s voice calling function to ring a target’s device. Even if the call was not picked up, the surveillance software would be installed, and, the FT reported, the call would often disappear from the device’s call log.
WhatsApp told the BBC its security team was the first to identify the flaw, and shared that information with human rights groups, selected security vendors and the US Department of Justice earlier this month.
“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 company said on Monday in a briefing document note for journalists.
The firm also published an advisory to security specialists, in which it described the flaw as: “A buffer overflow vulnerability in WhatsApp VOIP [voice over internet protocol] stack allowed remote code execution via specially crafted series of SRTCP [secure real-time transport protocol]
packets sent to a target phone number.”
Prof Alan Woodward from the University of Surrey said it was a “pretty old-fashioned” method of attack.
“In a buffer overflow, an app is allocated more memory than it actually needs, so it has space left in the memory. If you are able to pass some code through the app, you can run your own code in that area,” he explained.
“In VOIP there is an initial process that dials up and establishes the call, and the flaw was in that bit. Consequently you did not need to answer the call for the attack to work.”
Some users of the app have questioned why the app store notes associated with the latest update are not explicit about the fix.
