WhatsApp fixes dangerous flaw in Web app

The flaw could affect as many as 200 million people who use WhatsApp's web interface, wrote Oded Vanunu, Check Point's group manager for security research and penetration.

"All an attacker needed to do to exploit the vulnerability was to send a user a seemingly innocent vCard containing malicious code," he wrote.

The flaw was found by a Check Point researcher, Kasif Dekel. He found that the Web version of WhatsApp failed to properly filter electronic business cards in the vCard format.

Dekel found it was possible to change the file extension for a vCard to .bat, or a batch executable script. WhatsApp thinks a user is just receiving a vCard, but it's actually executable code.

"This means once the victim clicks the downloaded file (which he assumes is a contact card), the code inside the batch file runs on his computer," Dekel wrote.

An attacker just needs the victim's phone number to send the malicious code and for the recipient to accept it.

Check Point disclosed the flaw to WhatsApp on Aug. 21, and WhatApp released an update for Web clients on Aug. 27. The up-to-date version is v0.1.4481.

Check Point waited until Tuesday to publicly disclose the vulnerability.