CVE-2015-5900 in Mac OS X
Summary
by MITRE
The protected range register in the EFI component in Apple OS X before 10.11 has an incorrect value, which allows attackers to cause a denial of service (boot failure) via a crafted app that writes to an unintended address.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability identified as CVE-2015-5900 resides within the EFI (Extensible Firmware Interface) component of Apple's macOS operating system, specifically affecting versions prior to 10.11. This flaw manifests in the improper configuration of the protected range register, a critical hardware abstraction layer element that governs memory access permissions and security boundaries within the firmware environment. The protected range register serves as a fundamental security mechanism that defines which memory regions can be accessed by the operating system and which remain protected from unauthorized modifications. When this register contains an incorrect value, it creates a dangerous condition where the firmware fails to properly enforce memory protection boundaries.
The technical implementation of this vulnerability allows attackers to craft malicious applications that can write to memory addresses that should normally be protected or restricted. This occurs because the incorrect register value effectively disables or weakens the memory protection mechanisms that should prevent unauthorized writes to critical firmware regions. The flaw specifically targets the EFI firmware environment where the operating system transitions from firmware to the kernel, making it a critical point of attack. When an attacker successfully exploits this vulnerability, the malicious application can write to unintended memory addresses within the EFI protected range, potentially corrupting firmware structures or boot parameters that are essential for system operation.
The operational impact of CVE-2015-5900 is severe and directly manifests as a denial of service condition, specifically causing boot failures that render affected systems unable to start properly. This vulnerability represents a critical weakness in the system's boot integrity mechanism, as it allows attackers to compromise the firmware level security controls that protect against unauthorized modifications to the boot process. The attack vector requires only a crafted application that leverages the incorrect register value to perform unauthorized writes to protected memory regions, making it particularly dangerous as it can be executed without requiring elevated privileges or physical access to the system. This represents a significant bypass of the security model that should normally prevent such low-level modifications from occurring during normal system operation.
This vulnerability aligns with CWE-119, which describes weaknesses in memory management that allow improper access to memory regions, and represents a failure in the firmware security model that should prevent unauthorized modifications to protected system memory. The attack pattern follows the techniques described in the MITRE ATT&CK framework under the Tactic of Execution and Persistence, specifically targeting the boot process and firmware integrity. The vulnerability demonstrates a classic case of insufficient privilege separation between the firmware and operating system components, where the EFI environment fails to properly enforce memory protection boundaries that are fundamental to system security. Apple's resolution involved updating the EFI firmware implementation to correctly configure the protected range register values, ensuring that memory protection mechanisms function as intended and preventing unauthorized writes to critical system regions that could compromise the boot process and overall system integrity.
The broader implications of this vulnerability extend beyond simple denial of service, as it represents a fundamental failure in the firmware security architecture that could potentially enable more sophisticated attacks. The protected range register vulnerability exposes the underlying assumption that firmware-level memory protection controls are properly maintained and enforced, which is a critical element of the security model for modern operating systems. This flaw highlights the importance of proper firmware security implementation and the need for continuous auditing of low-level system components that operate outside the normal operating system security boundaries. The vulnerability also demonstrates the risks associated with insufficient validation of memory access permissions in firmware environments, where a single incorrectly configured register can compromise the entire boot process integrity and potentially enable further exploitation of the system.