Zoom lets a website turn on your Mac’s camera without permission

Video conferencing app Zoom has a major security flaw in its Mac client, letting any website turn on your Mac’s camera without a warning, security researcher Jonathan Leitschuh claims. 

In a blog post Monday, Leitschuh detailed the vulnerability, which he says he’d disclosed to Zoom more than 90 days ago, and the company still hasn’t fixed it. 

The problem lies in Zoom’s usage of a web server on users’ local machines. This makes some of Zoom’s cool features possible, for example, clicking on a simple link in your web browser automatically starts up the app. 

Having an app install and run a web server on a user’s machine with an undocumented API “feels incredibly sketchy,” Leitschuh says. But there’s more. According to Leitschuh, “this web server can do far more than just launch a Zoom meeting. (…) this web server can also re-install the Zoom app if a user has uninstalled it.”

This is bad by itself, but Leitschuh discovered a vulnerability that let him launch a Zoom call, with video enabled, on a user’s machine without permission. The same vulnerability allows the attacker to perform a DOS (denial of service) type attack on a user’s machine. 

Leitschuh says that he’d contacted Zoom on March 26, offering the company a quick fix for the vulnerability. After a lot of back and forth, Zoom partially fixed the flaw, but Leitschuh was able to bypass their fix, after which the company offered no additional fix. The security issue is still present in the latest version of Zoom for Mac, 4.4.4. 

In a blog post Monday, Zoom defended its app’s functionality, claiming that users are prompted to turn their video off when joining their first meeting, and can set the video to off in subsequent meetings; if they do so, it would be impossible for the host or other participants to turn their camera on. Furthermore, Zoom claims, “because the Zoom client user interface runs in the foreground upon launch, it would be readily apparent to the user that they had unintentionally joined a meeting and they could change their video settings or leave immediately.”

The company said they will give users more control of their video settings in an upcoming, July 2019 release. 

The company also addresses the presence of the web server on user machines, saying it’s a “workaround to a change introduced in Safari 12” and a “legitimate solution to a poor user experience problem.”

Zoom has assessed that both the video call issue and the DOS issue were “low risk,” which is why the company decided not to change the app’s functionality. The company also promised it will launch a public vulnerability disclosure program in the “next several weeks.”

The main question users should be asking themselves is whether they want to sacrifice their system’s security for a bit of added functionality — likely, functionality they can live without. Zoom’s ability to re-install itself without user permission after it’s been uninstalled is particularly worrisome. Since there’s no official fix for the issue, you can remove Zoom’s web server from your machine by following the steps described in Leitschuh’s post.