CVE-2016-3699 in Linux
Summary
by MITRE
The Linux kernel, as used in Red Hat Enterprise Linux 7.2 and Red Hat Enterprise MRG 2 and when booted with UEFI Secure Boot enabled, allows local users to bypass intended Secure Boot restrictions and execute untrusted code by appending ACPI tables to the initrd.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-3699 represents a critical security flaw in the Linux kernel implementation of UEFI Secure Boot mechanisms within Red Hat Enterprise Linux 7.2 and Red Hat Enterprise MRG 2 environments. This weakness specifically targets the integrity verification processes that are fundamental to preventing unauthorized code execution during system boot. The flaw manifests when systems are configured with UEFI Secure Boot enabled, creating a scenario where local attackers can circumvent the intended security controls that are designed to ensure only trusted operating system components can execute during the boot process.
The technical exploitation of this vulnerability occurs through the manipulation of ACPI (Advanced Configuration and Power Interface) tables within the initrd (initial ramdisk) environment. Attackers can append malicious ACPI tables to the initrd, effectively bypassing the Secure Boot restrictions that should prevent execution of untrusted code. This technique exploits a design oversight in how the kernel processes these tables during the boot sequence, allowing malicious code to be loaded and executed with the same privileges as legitimate system components. The vulnerability essentially creates a backdoor path through which untrusted code can be introduced and executed, undermining the fundamental security assumptions of the UEFI Secure Boot framework.
The operational impact of this vulnerability is severe and far-reaching within enterprise environments that rely on UEFI Secure Boot for system integrity protection. Local attackers who can access the system can leverage this flaw to execute arbitrary code with kernel-level privileges, potentially leading to complete system compromise. The vulnerability affects systems where UEFI Secure Boot is enabled, which is increasingly common in enterprise and government deployments where security compliance mandates such protections. This flaw essentially nullifies the security benefits that organizations expect from UEFI Secure Boot implementations, creating a persistent threat vector that can be exploited to establish persistent backdoors or escalate privileges.
Mitigation strategies for CVE-2016-3699 focus on both immediate patching and architectural modifications to prevent exploitation. Organizations should prioritize applying the relevant kernel updates provided by Red Hat that address this specific vulnerability by properly validating ACPI table contents within the initrd environment. Additionally, system administrators should consider disabling UEFI Secure Boot where possible, though this reduces overall security posture. The mitigation approach aligns with CWE-174 which addresses weaknesses in input validation and the broader ATT&CK framework category T1068 which covers exploit for privilege escalation. Network segmentation and monitoring for suspicious ACPI table modifications can serve as additional defensive measures, while regular security assessments should verify that no unauthorized modifications have occurred in the initrd environment.