Boot-health attestation bypass via unextended SHA256 PCRs
Published Oct 20, 2021 · Updated Aug 4, 2024
A TPM attestation bypass in Microsoft Surface Pro 3 BIOS 3.11.2550 and earlier allows physically proximate attackers to falsify boot health. When SHA1 and SHA256 PCR banks are enabled, the firmware extends only SHA1, leaving low SHA256 PCRs empty for attacker-supplied measurements. Exploitation requires physical control to boot an unmeasured operating system, after which the TPM can produce a valid quote for a fabricated healthy state.
Summary
What happened
A TPM attestation bypass in Microsoft Surface Pro 3 BIOS 3.11.2550 and earlier allows physically proximate attackers to falsify boot health. When SHA1 and SHA256 PCR banks are enabled, the firmware extends only SHA1, leaving low SHA256 PCRs empty for attacker-supplied measurements. Exploitation requires physical control to boot an unmeasured operating system, after which the TPM can produce a valid quote for a fabricated healthy state.
The record
- CVE
- CVE-2021-42299
- Published
- Oct 20, 2021
- Updated
- Aug 4, 2024
- Vendor
- Microsoft
- Product
- Microsoft Surface Pro 3
- Classifications
- T1211
- Attack vector
- physical
- Privileges
- authenticated
Timeline
How it unfolded
- Oct 20, 2021CVE publishedPublication date reported by the CVE source.
- Aug 4, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=N/A
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
- TPM Carte Blanche proof of conceptfunctional · demonstrated
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Technologies
Your stack
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Your stack
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