Two of the vulnerabilities — tracked as CVE-2021-3971 and CVE-2021-3972 — reside in UEFI firmware drivers intended for use only during the manufacturing process of Lenovo consumer notebooks. Lenovo engineers inadvertently included the drivers in the production BIOS images without being properly deactivated. Hackers can exploit these buggy drivers to disable protections, including UEFI secure boot, BIOS control register bits, and protected range register, which are baked into the serial peripheral interface (SPI) and designed to prevent unauthorized changes to the firmware it runs. After discovering and analyzing the vulnerabilities, researchers from security firm ESET found a third vulnerability, CVE-2021-3970. It allows hackers to run malicious firmware when a machine is put into system management mode, a high-privilege operating mode typically used by hardware manufacturers for low-level system management.
“All three of the Lenovo vulnerabilities discovered by ESET require local access, meaning that the attacker must already have control over the vulnerable machine with unfettered privileges,” notes Ars Technica’s Dan Goodin. “The bar for that kind of access is high and would likely require exploiting one or more critical other vulnerabilities elsewhere that would already put a user at considerable risk.”
Still, it’s worth looking to see if you have an affected model and, if so, patch your computer as soon as possible.