Microsoft Warns of New Safety Flaw Affecting Floor Professional 3 Gadgets

Microsoft Warns of New Security Flaw Affecting Surface Pro 3 Devices

Microsoft has printed a brand new advisory warning of a safety bypass vulnerability affecting Floor Professional 3 convertible laptops that could possibly be exploited by an adversary to introduce malicious units inside enterprise networks and defeat the machine attestation mechanism.

Tracked as CVE-2021-42299 (CVSS rating: 5.6), the problem has been codenamed “TPM Carte Blanche” by Google software program engineer Chris Fenner, who’s credited with discovering and reporting the assault approach. As of writing, different Floor units, together with the Floor Professional 4 and Floor E book, have been deemed unaffected, though different non-Microsoft machines utilizing an analogous BIOS could also be susceptible.

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“Gadgets use Platform Configuration Registers (PCRs) to report details about machine and software program configuration to make sure that the boot course of is safe,” the Home windows maker famous in a bulletin. “Home windows makes use of these PCR measurements to find out machine well being. A susceptible machine can masquerade as a wholesome machine by extending arbitrary values into Platform Configuration Register (PCR) banks.”

Nonetheless, it is value noting that pulling off an assault necessitates bodily entry to a goal sufferer’s machine, or {that a} dangerous actor has had beforehand compromised a respectable person’s credentials. Microsoft stated it has “tried” to inform all affected distributors.

Launched in Home windows 10, Machine Well being Attestation (DHA) is an enterprise safety characteristic that ensures consumer computer systems have reliable BIOS, Trusted Module Platform (TPM), and boot software program configurations enabled equivalent to early-launch antimalware (ELAM), Safe Boot, and way more. Put in a different way, DHA is designed to attest to the boot state of a Home windows pc.

The DHA service achieves this by reviewing and validating the TPM and PCR boot logs for a tool to concern what’s a tamper-resistant DHA report that describes how the machine began. However by weaponizing this flaw, attackers can corrupt the TPM and PCR logs to amass false attestations, successfully compromising the Machine Well being Attestation validation course of.

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“On a Floor Professional 3 operating latest platform firmware with SHA1 and SHA256 PCRs enabled, if the machine is booted into Ubuntu 20.04 LTS, there aren’t any measurements in any respect within the SHA256 financial institution low PCRs,” Fenner stated. “That is problematic as a result of this permits arbitrary, false measurements to be made (from Linux userland, for instance) comparable to any Home windows boot log desired. An trustworthy SHA256 PCR quote over dishonest measurements will be requested utilizing a respectable [Attestation Key] within the connected TPM.”

In a real-world state of affairs, CVE-2021-42299 will be abused to fetch a false Microsoft DHA certificates by acquiring the TCG Log — which information measurements made throughout a boot sequence — from a goal machine whose well being the attacker needs to impersonate, adopted by ship a legitimate well being attestation request to the DHA service.

Further technical particulars concerning the assault and a proof-of-concept (PoC) exploit will be accessed from Google’s Safety Analysis repository right here.

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