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Secured-Core PCs May Mitigate Firmware Attacks, but Adoption Lags

Microsoft maintains that exploitation of recent Dell vulnerabilities would be blocked on ultra-secure PCs - but most systems do not have the technology yet.

When firmware-security firm Eclyspium revealed four flaws last month in a Dell firmware utility that could allow attacks against the basic system software on laptops and other devices, the company maintained that vulnerabilities posed a significant threat to users of the systems.

Microsoft, however, has argued that laptops with the latest security-attestation technology, known as Secured Core, are not susceptible to such attacks because the technology was created with the assumption that the firmware is untrustworthy.

Secured-core PCs take a defense-in-depth approach to basic system security, a Microsoft spokesperson said in a statement sent to Dark Reading.

"The attack described in the published research circumvents protections provided by secure boot," Microsoft said. "However, secured-core PCs go a step further and implement System Guard firmware protection which helps protect sensitive assets stored in virtualization-based security, like credentials, from attacks that take advantage of firmware vulnerabilities to bypass features like secure boot."

The point is somewhat moot at present, however, as adoption of the Secured Core technology—originally announced in October 2019—still lags. Dell, which confirmed the vulnerabilities found by Eclypsium, only has 18 models of devices that support Secured Core, none of which has the technology installed by default, according to a note on Dell's official Secured-core PC page.

Eclypsium also refutes that secured-core PCs would be immune to such attacks.

"The attack works on Dell PCs including secured-core PCs and affects user data," John Loucaides, vice president of federal technology for Eclypsium, said in a statement to Dark Reading. "Microsoft's response is a strawman of our statements in order to divert attention from what we actually said."

In late June, Eclypsium announced that a firmware-update utility preinstalled on 128 models of Dell laptops, desktops, servers, and tablets had four vulnerabilities that could allow attackers to install malicious code. A privileged attacker with the ability to redirect traffic on the local network—either through controlling a router, ARP poisoning, or another technique—could use Dell's SupportAssist system utility.

The most significant vulnerability allows the attacker to impersonate Dell if they have the ability to direct traffic from the targeted system and compromise systems at the firmware level, if they are not protected by Secure Boot. Three other issues in Secure Boot allow attackers to circumvent that defense as well.

Microsoft secured-core technology "does nothing to prevent exploiting a vulnerability in UEFI firmware to achieve arbitrary code execution in the pre-boot environment and leveraging that to gain access to user data on the device or gain arbitrary code execution once a user logs into the system," Loucaides said. "We'll be providing more details at our DEF CON talk, including a video demonstrating this which we will show at DEF CON."

When asked if Secured Core would prevent the exploitation of Dell devices, Microsoft did not directly respond to that question but instead argued that even if the firmware is compromised, Secured Core would limit the damage.

"The System Guard feature in Secured-core PCs is designed to protect critical portions of the Windows OS and the keys and secrets that reside there specifically for cases like this where the firmware on a system is compromised," the company said in its statement to Dark Reading. "Microsoft's Credential Guard assumes the system has been tampered with and then relies on System Guard to protect the virtual container that isolates the identity of the user even in the event of an attack."

While Secured Boot has not gained widespread adoption yet—and Microsoft declined to give data on the technology's enterprise penetration—the company predicts that the technology will quickly make gains. Eventually, Secured Core will be required on new Windows systems.

"As the hardware and firmware baseline required by System Guard are increasingly met by more and more new systems we will see the number of Windows devices running System Guard increase," Microsoft stated. "At some point in the future all new Windows systems will be required to support it."

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