One click, frozen Mac

A WebGPU shader served by any untrusted site can hang a Mac's graphics until you force a restart. The victim only has to click a link.

“All the victim needs to do is click a link.”

Only Macs go down

It reproduces on Chrome, Firefox, and Safari under macOS, tested on M-series MacBooks running Tahoe. Other operating systems just chug and recover when you close the tab.

Built on WebGPU

WebGPU lets any site submit shaders straight to the device's GPU. It is the successor to WebGL and ships in every major browser.

A loop that never ends

The compute shader runs a for loop with no increment, copying the same vector in a buffer forever. Twelve lines of scaffolding around one runaway loop.

“// no i++, loop spins endlessly”

The render shader waits

The vertex shader reads from the same buffer the compute shader is busy writing. It can never move forward, so the GPU work piles up.

WindowServer goes down with it

The pileup spills into macOS's WindowServer. You get a beachball, a dead cursor, or magenta junk smeared across part of the screen.

“Sometimes I get the beachball, and sometimes magenta junk shows up on part of the screen.”

The machine is fine, the screen is not

You can still SSH in normally. But a watchdog sees WindowServer stop responding, triggers a kernel panic, and reboots the Mac.

“Interestingly, the rest of the computer is fine at this point.”

Apple fixed this in 2023

Ron Masas of Imperva did the same trick with WebGL in 2023. Apple issued CVE-2023-40441 at medium severity and added validation to catch runaway loops.

Loop detection cannot win

WebGPU's validation is weaker, and chasing infinite loops runs into the halting problem. The real fix is pre-empting unresponsive shaders, which every other OS already does.

“detecting infinite loops is a losing game; you can't get around the halting problem”

Blame the coprocessor

On M-series chips the kernel cannot pre-empt the GPU directly. All the pre-emption logic lives in firmware on a coprocessor called the ASC.

“The OS kernel cannot directly pre-empt the GPU.”

Apple says not a security issue

Disclosed July 27, 2026. Apple reproduced it and promised a fix, then reversed course on August 26, calling a hang or crash outside its definition of a security bug.

“the result is either a crash, hang, or recoverable data loss which we do not consider to be a security issue”