An old design flaw in the x86 processor architecture could allow attackers to install a rootkit in the low-level firmware of computers, a security researcher said Thursday. The vulnerability was disclosed Thursday at the Black Hat security conference by Christopher Domas, a security researcher with the Battelle Memorial Institute.

By leveraging the flaw, attackers could install a rootkit in the processor's System Management Mode (SMM), a protected region of code that underpins all the firmware security features in modern computers.

Once installed, the rootkit could be used for destructive attacks like wiping the UEFI (Unified Extensible Firmware Interface) the modern BIOS or even to re-infect the OS after a clean install. Protection features like Secure Boot wouldn't help, because they, too rely on the SMM to be secure.

According to Domas, Intel is aware of the issue and has mitigated it in its latest CPUs. The company is also rolling out firmware updates for older processors, but not all of them can be patched, he said.

To exploit the vulnerability and install the rootkit, attackers would already need to have kernel or system privileges on a computer. That means the flaw can't be used by itself to compromise a system, but could make an existing malware infection highly persistent and completely invisible.