CVE-2019-8606 in macOS
Summary
by MITRE
A validation issue existed in the handling of symlinks. This issue was addressed with improved validation of symlinks. This issue is fixed in macOS Mojave 10.14.5. A local user may be able to load unsigned kernel extensions.
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Analysis
by VulDB Data Team • 06/10/2020
The vulnerability identified as CVE-2019-8606 represents a critical validation flaw in macOS Mojave's handling of symbolic links within the kernel extension loading mechanism. This issue stems from insufficient validation checks that allow malicious actors to exploit the system's trust model when processing symbolic link references. The flaw specifically affects how the operating system validates symlink paths during kernel extension loading processes, creating a potential attack vector for privilege escalation. The vulnerability is categorized under CWE-59, which addresses improper handling of symbolic links, and aligns with ATT&CK technique T1543.003 for creating or modifying system level persistence through kernel extensions.
The technical implementation of this vulnerability allows a local attacker to manipulate symbolic link references in a manner that bypasses normal kernel extension validation procedures. When the system processes kernel extensions, it fails to properly validate the integrity and legitimacy of symbolic link targets, enabling attackers to redirect extension loading to malicious payloads. This issue particularly impacts the kernel extension loading framework where symbolic links are used to reference extension locations, creating a path traversal scenario that can be exploited to load unsigned kernel extensions. The flaw essentially undermines the system's ability to verify that kernel extensions originate from legitimate sources and have not been tampered with during the loading process.
The operational impact of CVE-2019-8606 extends beyond simple privilege escalation to encompass potential system compromise and persistent access. A local user who successfully exploits this vulnerability can load unsigned kernel extensions, effectively bypassing macOS security controls designed to prevent unauthorized kernel code execution. This capability enables attackers to gain root-level privileges and establish persistent backdoors within the system. The attack surface is particularly concerning because it leverages the legitimate kernel extension loading mechanism, making malicious activity harder to detect through traditional security monitoring approaches. The vulnerability affects systems running macOS Mojave versions prior to 10.14.5, where the patch was implemented to address the symlink validation shortcomings.
Mitigation strategies for CVE-2019-8606 focus on immediate system updates and enhanced monitoring of kernel extension loading activities. Organizations should prioritize updating affected macOS systems to version 10.14.5 or later, which incorporates improved symlink validation mechanisms. System administrators should implement enhanced monitoring of kernel extension loading processes and establish baseline behavior for legitimate extension loading to detect anomalous activities. The fix addresses the root cause by implementing stricter validation of symbolic link targets during kernel extension loading, ensuring that all referenced paths are properly verified before extension execution. Additional protective measures include enabling System Integrity Protection, implementing strict file permission controls, and conducting regular security audits of kernel extension installations to prevent unauthorized modifications to system critical components.