CVE-2014-3677 in Shim
Summary
by MITRE
Unspecified vulnerability in Shim might allow attackers to execute arbitrary code via a crafted MOK list, which triggers memory corruption.
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Analysis
by VulDB Data Team • 03/30/2022
The vulnerability identified as CVE-2014-3677 resides within the Shim bootloader component that serves as a critical interface between the Unified Extensible Firmware Interface and the operating system during the boot process. This flaw exists within the Machine Owner Key management system which is integral to the Secure Boot implementation in UEFI firmware environments. The vulnerability specifically manifests when the Shim bootloader processes a maliciously crafted Machine Owner Key list that can trigger memory corruption conditions during the verification and execution phases of the boot sequence.
The technical exploitation of this vulnerability occurs through the manipulation of the MOK list structure which is used to manage trusted keys for Secure Boot enforcement. When Shim encounters a crafted MOK list, it fails to properly validate the memory allocation and processing of the key data structures, leading to potential buffer overflows or memory corruption scenarios. This memory corruption can be leveraged by attackers to overwrite critical memory locations and ultimately execute arbitrary code with the privileges and access levels of the bootloader itself. The flaw represents a classic memory safety issue that enables privilege escalation from the bootloader context to potentially full system compromise.
The operational impact of this vulnerability extends far beyond simple code execution capabilities as it fundamentally undermines the security model of Secure Boot implementations across numerous operating systems including various versions of Microsoft Windows and Linux distributions. Attackers who successfully exploit this vulnerability can bypass the entire boot process security chain, potentially allowing them to load malicious code before the operating system has fully initialized. This creates a persistent threat vector that can survive traditional operating system security measures and can be particularly devastating in enterprise environments where Secure Boot is relied upon for endpoint protection. The vulnerability affects systems where Shim is used for Secure Boot enforcement and can be exploited through various attack vectors including physical access or network-based delivery of malicious firmware updates.
Mitigation strategies for CVE-2014-3677 should prioritize immediate patching of affected Shim bootloader implementations and firmware updates from hardware vendors. Organizations should implement strict firmware update policies that validate the integrity of all bootloader components through cryptographic signatures before deployment. The implementation of additional runtime protections such as kernel module signing enforcement and memory protection mechanisms can provide defense-in-depth against exploitation attempts. System administrators should also monitor for unauthorized firmware modifications and implement hardware-based security features like Intel TXT or AMD SEV when available. This vulnerability aligns with CWE-121 and CWE-122 categories related to buffer overflow conditions and memory corruption issues, and represents a technique that can be mapped to ATT&CK tactics including TA0002 (Execution) and TA0004 (Privilege Escalation) through the exploitation of bootloader-level security controls. Organizations should conduct comprehensive inventory assessments to identify all systems running affected Shim versions and establish automated monitoring for potential exploitation attempts.