CVE-2017-16837 in Trusted Boot
Summary
by MITRE
Certain function pointers in Trusted Boot (tboot) through 1.9.6 are not validated and can cause arbitrary code execution, which allows local users to overwrite dynamic PCRs of Trusted Platform Module (TPM) by hooking these function pointers.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-16837 resides within the Trusted Boot framework known as tboot version 1.9.6 and earlier, representing a critical security flaw that undermines the integrity of the Trusted Platform Module (TPM) infrastructure. This issue specifically targets the validation mechanisms of function pointers within the tboot implementation, creating a pathway for malicious actors to exploit the system's trust model. The vulnerability's impact extends beyond simple code execution, as it enables attackers to manipulate the dynamic PCRs of the TPM, which are critical components responsible for maintaining the platform's integrity measurements. The flaw exists in the way tboot handles function pointer validation during its boot process, where it fails to properly verify the legitimacy of these pointers before execution, thereby opening the door for unauthorized modifications to the platform's trusted state.
The technical exploitation of this vulnerability occurs through a sophisticated attack vector that leverages local user privileges to hook and overwrite function pointers within the tboot environment. When these unvalidated function pointers are invoked, they can redirect execution flow to malicious code that has been carefully crafted to manipulate the TPM's dynamic PCRs. This manipulation allows attackers to alter the platform's integrity measurements, effectively bypassing the security mechanisms that TPMs are designed to enforce. The vulnerability directly relates to CWE-823, which describes the weakness of using invalid pointers, and can be mapped to ATT&CK technique T1495, which involves virtualization and sandbox evasion through manipulation of system components. The flaw particularly affects the integrity verification process of the Trusted Platform Module, where the dynamic PCRs serve as measurement registers that capture the state of the boot process and system configuration, making them prime targets for manipulation.
The operational impact of CVE-2017-16837 is severe and far-reaching, as it fundamentally compromises the security posture of systems relying on tboot for trusted boot processes. Attackers who successfully exploit this vulnerability can effectively subvert the entire Trusted Platform Module infrastructure, potentially enabling them to bypass secure boot mechanisms, manipulate system integrity measurements, and establish persistent backdoors within the platform. This compromise undermines the core principles of trusted computing, where the TPM is expected to provide immutable measurements of the system's state and detect any unauthorized modifications. The vulnerability's exploitation can lead to complete system compromise, as attackers can manipulate the boot process to load malicious code while maintaining the illusion of system integrity. Organizations using tboot versions 1.9.6 or earlier face significant risks, as this flaw allows for stealthy attacks that can evade traditional security monitoring mechanisms while simultaneously undermining the cryptographic foundations that secure boot processes depend upon.
Mitigation strategies for CVE-2017-16837 require immediate attention and should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves upgrading to tboot version 1.9.7 or later, which includes proper validation of function pointers and addresses the core flaw in the Trusted Boot implementation. Organizations should also implement comprehensive monitoring of TPM dynamic PCR values to detect unauthorized modifications and establish robust integrity measurement processes that can identify when the system's trust model has been compromised. Additional mitigations include hardening the boot environment through secure boot policies, implementing proper access controls to limit local user privileges, and deploying intrusion detection systems that can monitor for suspicious function pointer manipulation patterns. The vulnerability highlights the importance of proper input validation and pointer integrity checks in security-critical code, as outlined in the OWASP Top 10 and other security frameworks that emphasize the need for robust validation mechanisms in trusted computing environments.