CVE-2018-6622 in Trusted Platform Module
Summary
by MITRE
An issue was discovered that affects all producers of BIOS firmware who make a certain realistic interpretation of an obscure portion of the Trusted Computing Group (TCG) Trusted Platform Module (TPM) 2.0 specification. An abnormal case is not handled properly by this firmware while S3 sleep and can clear TPM 2.0. It allows local users to overwrite static PCRs of TPM and neutralize the security features of it, such as seal/unseal and remote attestation.
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Analysis
by VulDB Data Team • 03/16/2020
The vulnerability identified as CVE-2018-6622 represents a critical flaw in TPM 2.0 firmware implementations that affects a broad range of system manufacturers. This issue stems from how firmware producers interpret a specific section of the Trusted Computing Group's TPM 2.0 specification, particularly concerning the handling of abnormal cases during S3 sleep operations. The flaw manifests when systems enter and resume from S3 sleep states, creating a scenario where TPM 2.0 state management fails catastrophically. This vulnerability operates at the intersection of hardware security and firmware design, fundamentally undermining the trust model that TPMs are designed to provide.
The technical root cause of this vulnerability lies in improper handling of edge cases during system power state transitions, specifically when transitioning through S3 sleep mode. During these transitions, the TPM firmware fails to properly manage the state of static Platform Configuration Registers, which are critical for maintaining the integrity of the platform's security posture. When the system resumes from S3 sleep, the firmware does not correctly restore or validate the static PCR values, leading to their complete clearing. This behavior directly violates the fundamental principles of TPM 2.0 specification, which mandates that static PCRs should maintain their values across system transitions to preserve the platform's security state. The vulnerability is classified under CWE-248, representing an improper exception handling scenario, and aligns with ATT&CK technique T1499.001 for data destruction through system firmware manipulation.
The operational impact of CVE-2018-6622 is severe and far-reaching, as it completely neutralizes the core security features that TPM 2.0 implementations provide. When static PCRs are cleared, the system loses its ability to perform proper seal/unseal operations, which are essential for secure credential storage and platform authentication. Additionally, remote attestation capabilities become compromised, as the TPM cannot provide valid measurements of the system's state to external parties. This vulnerability creates a persistent security weakness that can be exploited by local attackers to bypass security mechanisms, potentially allowing unauthorized access to protected data and systems. The impact extends beyond individual system security to affect entire enterprise environments where TPM-based security controls are deployed, as the cleared PCRs cannot be easily restored without complete system reinitialization.
Mitigation strategies for CVE-2018-6622 require a multi-layered approach combining firmware updates, system configuration changes, and operational procedures. System administrators should prioritize applying firmware patches provided by manufacturers, as these updates specifically address the improper exception handling during S3 sleep transitions. Organizations should also consider disabling S3 sleep functionality on affected systems until proper patches are deployed, though this may impact power efficiency and user experience. Security monitoring should be enhanced to detect unusual TPM state changes and PCR modifications, as these could indicate exploitation attempts. The vulnerability highlights the importance of rigorous firmware testing and validation processes, particularly for security-critical components, and underscores the need for better adherence to established security standards and specifications. Regular security assessments should include TPM state validation checks to ensure that platform configuration registers maintain their integrity across system transitions.