A hidden CPU core in x86 chips bypasses kernel security

A security researcher exposed a hardware backdoor in certain x86 processors that lets regular user apps bypass operating system security controls entirely.

Security researcher Domas (@xoreaxeaxeax) published project:rosenbridge, revealing a secret core embedded alongside the main x86 CPU. By sending custom instructions to this hidden core, unprivileged userland apps can directly read and write kernel data. While enabling the backdoor should require root privileges, researchers found it enabled by default on some systems.

Why it matters: This isn't a simple software bug—it's a hardware-level bypass that ignores every privilege check built into the CPU. The affected VIA C3 processors are used across industrial hardware, ATMs, point-of-sale systems, and medical devices.

Try it / know this: You can test your hardware by running ./bin/check on bare metal using the tool in the rosenbridge repository, which also offers a boot script to close the backdoor.

Generations of chips after the C3 dropped this hidden feature, but it's a wild case study in how hardware features can turn into uninvited front doors.