CVE-2020-3908 in macOS
Summary
by MITRE
An out-of-bounds read was addressed with improved input validation. This issue is fixed in macOS Catalina 10.15.4. A local user may be able to cause unexpected system termination or read kernel memory.
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Analysis
by VulDB Data Team • 10/05/2020
The vulnerability identified as CVE-2020-3908 represents a critical out-of-bounds read flaw within the macOS kernel that could potentially compromise system stability and security. This issue affects macOS Catalina versions prior to 10.15.4, where improper input validation allows malicious local users to exploit a fundamental memory access violation. The vulnerability stems from insufficient bounds checking in kernel-level code, creating an opportunity for attackers to manipulate memory access patterns beyond allocated boundaries. Such flaws typically arise when developers fail to validate input parameters or buffer limits before processing data within kernel space, leading to unpredictable behavior that can result in system crashes or unauthorized memory access. The root cause aligns with CWE-129, which specifically addresses insufficient validation of length of inputs, and CWE-787, which covers out-of-bounds write operations that can occur when buffer boundaries are not properly enforced. This vulnerability exists within the kernel execution context, making it particularly dangerous as it operates with the highest privilege levels and can potentially expose sensitive kernel memory structures to unauthorized access.
The operational impact of CVE-2020-3908 extends beyond simple system instability to encompass potential information disclosure and system compromise scenarios. When exploited, the out-of-bounds read can cause unexpected system termination through kernel panic conditions, effectively rendering the affected system unusable until reboot. More concerning is the potential for kernel memory reading, which could expose sensitive information including cryptographic keys, user credentials, or other confidential data stored in kernel memory. Attackers leveraging this vulnerability could craft malicious payloads that trigger the out-of-bounds condition and subsequently read adjacent memory locations to extract valuable information. The local nature of this exploit means that an attacker must already have user-level access to the system, but the privilege escalation potential makes it particularly attractive for adversaries seeking to gain deeper system control. This vulnerability aligns with ATT&CK technique T1068, which covers local privilege escalation, and T1005, covering data from local system, as it enables both system stability disruption and information extraction capabilities.
The mitigation for CVE-2020-3908 primarily involves updating to macOS Catalina 10.15.4 or later versions where Apple has implemented improved input validation mechanisms to prevent the out-of-bounds read condition. System administrators should prioritize deployment of this security update across all affected macOS systems, particularly those handling sensitive data or operating in enterprise environments. Additional defensive measures include implementing kernel extension whitelisting policies, monitoring for unusual system termination patterns, and maintaining robust endpoint detection and response capabilities to identify potential exploitation attempts. Organizations should also consider implementing network-based intrusion detection systems to monitor for anomalous behavior that might indicate exploitation attempts. The fix addresses the underlying input validation weakness by implementing proper bounds checking mechanisms that ensure all memory access operations remain within allocated buffer boundaries. Security teams should conduct vulnerability assessments to confirm all macOS systems have been patched and monitor for any exploitation attempts targeting this specific vulnerability. This remediation approach follows established security best practices for kernel-level vulnerability management and aligns with industry standards for preventing memory corruption vulnerabilities that could lead to privilege escalation or information disclosure.