Linux Mint fixes screensaver bypass discovered by two kids

Two children playing on their dad's computer accidentally found a way to bypass the screensaver and access locked systems.
Written by Catalin Cimpanu, Contributor

The Linux Mint project has patched this week a security flaw that could have allowed a threat actor to bypass the OS screensaver and its password and access locked desktops.

This particularly nasty security flaw was discovered by two kids playing on their dad's computer, according to a bug report on GitHub.

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"A few weeks ago, my kids wanted to hack my Linux desktop, so they typed and clicked everywhere while I was standing behind them looking at them play," wrote a user identifying themselves as robo2bobo.

According to the bug report, the two kids pressed random keys on both the physical and on-screen keyboards, which eventually led to a crash of the Linux Mint screensaver, allowing the two access to the desktop.

"I thought it was a unique incident, but they managed to do it a second time," the user added.

Bug source: Pressing the ē key on the OSK

According to Linux Mint lead developer Clement Lefebvre, the issue was eventually tracked down to libcaribou, the on-screen keyboard (OSK) component that ships with Cinnamon, the desktop interface used by Linux Mint.

More specifically, the bug occurs when users press the "ē" key on the on-screen keyboard.

But while in most scenarios, the bug crashes the Cinnamon desktop process, if the on-screen keyboard is opened from the screensaver, the bug crashes the screensaver instead, allowing users to access the underlying desktop.

Lefebvre said the bug was introduced in the Linux Mint OS when the project patched another vulnerability last October, tracked as CVE-2020-25712.

Since then, all Linux Mint distributions using a Cinnamon version of 4.2 and later are vulnerable to this bypass. Cinnamon 4.2 is where the on-screen keyboard was added to the screensaver page.

patch was released this week, on Wednesday, that addresses the bug and prevents future crashes.

Lefebvre said the Linux Mint project is now working on adding a setting that will let users disable the on-screen keyboard, which would make mitigating future bugs in this component easier until patches are generally available.

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