CVE-2016-1796 in Mac OS X
Summary
by MITRE
Apple Type Services (ATS) in Apple OS X before 10.11.5 allows attackers to obtain sensitive kernel memory-layout information or cause a denial of service (out-of-bounds memory access) via a crafted app.
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Analysis
by VulDB Data Team • 08/19/2022
Apple Type Services represents a critical component within Apple's operating system architecture responsible for font handling and text rendering operations across the system. The vulnerability exists within the kernel-level processing of font data structures, specifically in how ATS manages memory allocation and access during font parsing operations. This flaw enables malicious actors to manipulate font files in ways that trigger improper memory handling within the kernel space, creating potential pathways for information disclosure or system instability. The vulnerability affects Apple OS X versions prior to 10.11.5, where the memory management controls for font processing were insufficiently hardened against malformed input data.
The technical exploitation of this vulnerability occurs through crafted font files that contain specially constructed data structures designed to trigger out-of-bounds memory access patterns within the Apple Type Services kernel extension. When the system processes these malicious font files, the ATS component fails to properly validate font data boundaries, leading to memory corruption that can either reveal kernel memory layout information or cause system crashes. This type of vulnerability falls under the CWE-125 Out-of-bounds Read classification, where the system reads memory locations beyond the intended buffer boundaries. The attack vector involves legitimate font processing workflows that are commonly used throughout the operating system, making the exploitation particularly stealthy and difficult to detect through normal security monitoring.
The operational impact of this vulnerability extends beyond simple denial of service conditions to include potential information disclosure that could aid in more sophisticated exploitation attempts. Attackers who successfully exploit this vulnerability can gain knowledge of kernel memory layouts, which serves as a crucial stepping stone for advanced persistent threats. The memory layout information obtained through this vulnerability can be used to bypass kernel address space layout randomization defenses and other security mitigations that rely on unpredictable memory arrangements. This makes the vulnerability particularly dangerous in targeted attack scenarios where adversaries are seeking to establish persistent access to systems. The vulnerability also enables denial of service conditions that can disrupt normal system operations and potentially cause system crashes that require manual intervention.
Mitigation strategies for this vulnerability require immediate system updates to Apple OS X version 10.11.5 or later, where Apple has implemented proper bounds checking and memory validation controls within the ATS component. System administrators should also implement proactive monitoring for unusual font processing activities and consider restricting font file processing in high-security environments. The vulnerability demonstrates the importance of kernel-level security controls and proper input validation in system components that handle user-supplied data. Organizations should also consider implementing application whitelisting policies that restrict font processing to known good applications and validate all font files before processing. This vulnerability aligns with ATT&CK technique T1059.007 for kernel-mode rootkits and T1068 for local privilege escalation through kernel exploits, highlighting the need for comprehensive security measures beyond traditional endpoint protection.