CVE-2016-1737 in Mac OS X
Summary
by MITRE
Carbon in Apple OS X before 10.11.4 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted .dfont file.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2016-1737 represents a critical memory corruption flaw within the Carbon framework of Apple's macOS operating system. This issue affects versions prior to macOS 10.11.4 and stems from improper handling of crafted .dfont font files during the font processing pipeline. The Carbon framework serves as a legacy application programming interface that provides essential system services for macOS applications, making this vulnerability particularly dangerous as it can be exploited through common font file interactions. The flaw manifests when the system attempts to parse maliciously constructed .dfont files, which are Apple's proprietary font format that can contain multiple font faces within a single file structure.
The technical implementation of this vulnerability resides in the memory management routines of the Carbon framework's font handling subsystem. When processing a specially crafted .dfont file, the system fails to properly validate input parameters and buffer boundaries, leading to memory corruption that can be leveraged by attackers to execute arbitrary code with the privileges of the affected process. This memory corruption typically occurs through buffer overflows or use-after-free conditions that arise from inadequate bounds checking during font data parsing operations. The vulnerability's exploitation requires minimal user interaction since font files are commonly encountered during system operations, making it particularly attractive to threat actors seeking to deliver malware through seemingly benign file attachments or web content.
The operational impact of CVE-2016-1737 extends beyond simple code execution, as it can also enable denial of service conditions that may compromise system stability and availability. Attackers can craft .dfont files that cause system crashes, application hangs, or complete system reboots, effectively creating a persistent availability threat. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates how legacy frameworks can harbor critical security flaws that persist across multiple system versions. The attack surface is broad as .dfont files can be encountered in various contexts including email attachments, web downloads, and software installations, making the exploitation vector highly accessible to remote attackers. The vulnerability also maps to ATT&CK technique T1059.007 for command and control communication and T1203 for legitimate program execution, as successful exploitation can lead to persistent access and further system compromise.
Mitigation strategies for CVE-2016-1737 primarily focus on immediate system updates to macOS 10.11.4 or later versions where Apple has implemented proper input validation and memory safety controls. Organizations should prioritize patch management processes to ensure all macOS systems receive the security updates promptly, as the vulnerability exists in the core system frameworks that are difficult to isolate through traditional network security controls. Additional defensive measures include implementing strict file type filtering for font files, especially in enterprise environments where user behavior may be less controlled, and monitoring for unusual system behavior that could indicate exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date legacy framework security and demonstrates how older system components can remain vulnerable even when newer applications are secure, making comprehensive system hygiene essential for preventing exploitation.