CVE-2016-4779 in macOS
Summary
by MITRE
Apple Type Services (ATS) in Apple OS X before 10.12 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted font file.
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Analysis
by VulDB Data Team • 09/20/2022
Apple Type Services represents a critical component within Apple's operating system that handles font rendering and processing for graphical user interfaces. This vulnerability exists in Apple OS X versions prior to 10.12 where the ATS subsystem fails to properly validate font files before processing them. The flaw allows remote attackers to craft malicious font files that, when processed by the system, trigger memory corruption issues. These memory corruption vulnerabilities typically arise from improper bounds checking or buffer overflow conditions within the font parsing code that handles various font formats including TrueType, OpenType, and PostScript fonts.
The technical exploitation of this vulnerability occurs when a malicious font file is loaded by the operating system through normal user interactions such as browsing web pages, opening email attachments, or viewing documents that contain embedded fonts. The ATS service processes these font files without adequate sanitization, leading to memory corruption that can be leveraged to execute arbitrary code with the privileges of the affected process. This typically requires the attacker to craft a font file that exploits specific memory layout issues or pointer manipulation flaws within the ATS parser. The vulnerability's remote nature means attackers can exploit it without requiring physical access to the target system, making it particularly dangerous in web browsing scenarios where users might unknowingly encounter malicious fonts.
From an operational impact perspective, this vulnerability creates a significant risk for users who frequently browse the internet or handle untrusted documents containing embedded fonts. Attackers can leverage this flaw to gain unauthorized code execution capabilities, potentially leading to full system compromise. The denial of service aspect of this vulnerability means that even if code execution is not achieved, attackers can still cause system instability by triggering memory corruption that results in application crashes or system hangs. This vulnerability affects not only individual users but also enterprise environments where users might encounter malicious fonts through various attack vectors including phishing emails, compromised websites, or malicious documents. The widespread use of font rendering in modern operating systems means that exploitation can occur in numerous legitimate contexts, increasing the attack surface significantly.
The vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 for command and scripting interpreter, T1068 for exploit for privilege escalation, and T1203 for exploitation of remote services. Organizations should immediately apply the security patches released by Apple for OS X 10.12 and later versions. System administrators should also implement network-level protections such as web application firewalls that can detect and block suspicious font file content. Additionally, user education regarding safe browsing practices and avoiding untrusted sources remains crucial. Regular system updates and patch management procedures should be enforced to prevent exploitation of similar vulnerabilities in the future. The vulnerability demonstrates the importance of proper input validation and memory safety practices in system components that handle user-provided data, particularly those with broad system integration like font rendering services.