CVE-2020-9939 in macOS
Summary
by MITRE • 10/23/2020
This issue was addressed with improved checks. This issue is fixed in macOS Catalina 10.15.6. A local user may be able to load unsigned kernel extensions.
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Analysis
by VulDB Data Team • 11/26/2020
The vulnerability described in CVE-2020-9939 represents a significant security flaw in Apple's macOS operating system that allowed unauthorized kernel extension loading. This issue specifically affected systems running macOS Catalina versions prior to 10.15.6, creating a potential pathway for malicious actors to execute arbitrary code at the kernel level. The vulnerability stems from insufficient validation mechanisms that should have prevented the loading of unsigned kernel extensions, which are critical system components that operate with the highest privileges and can directly interact with hardware and core operating system functions.
The technical flaw manifests in the kernel extension loading mechanism where the system failed to properly verify the digital signatures of kernel extensions before permitting their execution. This weakness creates a scenario where a local attacker with basic system access could potentially craft or obtain unsigned kernel extensions and load them into the kernel space. Such unauthorized kernel extensions could then execute with elevated privileges, bypassing normal security controls and potentially enabling complete system compromise. The vulnerability directly relates to CWE-1104 which addresses the lack of proper validation of kernel code integrity and the absence of robust signature verification mechanisms in kernel space operations.
The operational impact of this vulnerability extends beyond simple privilege escalation as it fundamentally undermines the security model of macOS. Kernel extensions operate with the highest system privileges and can access all system resources, making them prime targets for attackers seeking persistent access or privilege elevation. An attacker exploiting this vulnerability could potentially install rootkits, modify system integrity checks, or establish backdoors that persist across reboots. The local nature of the attack means that any user with login access to the system could potentially exploit this flaw, making it particularly dangerous in multi-user environments or systems where user accounts might be compromised through social engineering or other means.
The fix implemented by Apple in macOS Catalina 10.15.6 addresses this vulnerability through enhanced kernel extension validation checks that enforce strict signature verification before any kernel extension can be loaded. This update aligns with industry best practices for kernel security and follows the ATT&CK framework's T1543.003 technique for creating or modifying system level persistence by ensuring that only properly signed and verified kernel extensions can execute. Organizations should prioritize updating to macOS 10.15.6 or later versions to remediate this vulnerability, as the risk of exploitation remains significant given the potential for complete system compromise through unauthorized kernel extension loading. The fix demonstrates Apple's commitment to addressing kernel-level security issues and reinforces the importance of maintaining up-to-date system software to protect against known vulnerabilities.