CVE-2015-6993 in Mac OS X
Summary
by MITRE
FontParser in Apple iOS before 9.1 and OS X before 10.11.1 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted font file, a different vulnerability than CVE-2015-6976, CVE-2015-6977, CVE-2015-6978, CVE-2015-6990, CVE-2015-6991, CVE-2015-7008, CVE-2015-7009, CVE-2015-7010, and CVE-2015-7018.
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Analysis
by VulDB Data Team • 11/19/2024
The vulnerability identified as CVE-2015-6993 represents a critical memory corruption flaw within Apple's FontParser component that affected iOS versions prior to 9.1 and OS X versions prior to 10.11.1. This vulnerability resides in the font handling subsystem that processes various font formats including TrueType, OpenType, and other embedded font types commonly used in digital documents and applications. The flaw manifests when the system processes maliciously crafted font files that contain specially constructed data structures designed to trigger buffer overflows or memory corruption conditions during parsing operations. This vulnerability operates at the intersection of multiple cybersecurity domains including software security, memory management, and application sandboxing mechanisms.
The technical implementation of this vulnerability involves improper bounds checking and memory allocation handling within the font parsing logic. When a malicious font file is processed, the FontParser fails to properly validate the size parameters and structure elements of the font data, leading to situations where memory allocated for font metadata or glyph information can be overwritten or accessed beyond its intended boundaries. This memory corruption can occur during various parsing operations including font header validation, glyph table processing, or metadata extraction phases. The vulnerability is particularly dangerous because it can be triggered through multiple attack vectors including email attachments, web content, or downloaded documents that contain embedded fonts, making it a prime target for exploit development.
The operational impact of CVE-2015-6993 extends beyond simple denial of service conditions to encompass full arbitrary code execution capabilities. Attackers can leverage this vulnerability to execute malicious payloads with the privileges of the affected application, potentially leading to complete system compromise. The memory corruption effects can result in unpredictable behavior including application crashes, system instability, or more critically, the ability to inject and execute arbitrary code within the context of the font processing application. This vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates the classic attack pattern where improper memory management leads to privilege escalation opportunities. The attack surface is particularly broad given that font files are commonly encountered in legitimate document processing, web browsing, and email systems.
Mitigation strategies for CVE-2015-6993 require immediate system updates to the patched versions of iOS 9.1 and OS X 10.11.1, which contain corrected font parsing routines with proper bounds checking and memory management. Organizations should implement comprehensive patch management procedures to ensure all affected systems receive updates promptly. Network administrators should consider implementing content filtering measures to prevent the delivery of potentially malicious font files through email systems and web proxies. Security teams should monitor for indicators of compromise related to font-based attacks and implement application whitelisting policies where possible. The vulnerability demonstrates the importance of proper input validation and memory safety practices as outlined in the MITRE ATT&CK framework under the T1059.007 technique for process injection and T1068 for exploit development. System hardening measures including sandboxing of font processing components and reduced privilege execution contexts can further mitigate the risk associated with this class of vulnerability.