A design flaw in the x86 processor architecture dating back almost two decades could allow attackers to install a rootkit in the low-level firmware of computers, a security researcher said Thursday. Such malware could be undetectable by security products.

The vulnerability stems from a feature first added to the x86 architecture in 1997. It 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 processors 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 wouldnt help, because they too rely on the SMM to be secure.

The attack essentially breaks the hardware roots of trust, Domas said.

Intel did not immediately respond to a request for comment. According to Domas, the chip maker 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 need to already have kernel or system privileges on a computer. That means the flaw cant be used by itself to compromise a system, but could make an existing malware infection highly persistent and completely invisible.

Domas only tested the exploit successfully on Intel processors, but noted that x86 processors made by AMD should in theory be vulnerable as well.

Even if BIOS/UEFI updates are made available by computer manufacturers, their rate of adoption is likely to be very low, especially among consumers.

Unfortunately theres not much users can do, except try not to become infected by malware in the first place that could gain kernel privileges to deploy such a rootkit.