CVE-2015-6977 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-2015-6978, CVE-2015-6990, CVE-2015-6991, CVE-2015-6993, 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-2015-6977 represents a critical memory corruption flaw within Apple's FontParser component that affects iOS versions prior to 9.1 and OS X versions prior to 10.11.1. This vulnerability resides in the font parsing functionality that processes various font formats including TrueType, OpenType, and other rasterization formats used by Apple's operating systems. The flaw specifically manifests when the system attempts to parse maliciously crafted font files, creating a potential attack vector for remote code execution or denial of service conditions. The vulnerability operates at the kernel level within Apple's graphics rendering subsystem, making it particularly dangerous as it can be exploited through various attack surfaces including email attachments, web downloads, and malicious websites.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the FontParser module. When processing font files, the parser fails to properly validate the structure and bounds of font data, leading to buffer overflows and memory corruption issues. This type of vulnerability maps directly to CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios. The parser's failure to implement proper bounds checking mechanisms allows attackers to craft font files with maliciously structured data that, when processed, overwrites adjacent memory locations. The memory corruption can result in arbitrary code execution if the attacker can control the overwritten memory regions, or cause a system crash leading to denial of service when the parser encounters malformed data structures.
From an operational perspective, this vulnerability presents significant risk to enterprise and individual users alike as font files are commonly encountered through multiple attack vectors. The remote exploitation capability means that attackers can deliver malicious payloads through web-based attacks without requiring user interaction beyond visiting a compromised website. This vulnerability is particularly concerning because font files are frequently embedded in various document formats, web content, and system applications, creating numerous potential entry points for exploitation. The impact extends beyond simple code execution as the memory corruption can cause system instability, leading to unpredictable behavior and potential data loss. Attackers leveraging this vulnerability could gain full system control or disrupt service availability, making it a prime target for advanced persistent threats and zero-day exploits.
The mitigation strategies for CVE-2015-6977 should prioritize immediate system updates to the patched versions of iOS 9.1 and OS X 10.11.1, which contain the necessary security fixes. Organizations should implement proactive measures including network segmentation to limit exposure, web filtering to block suspicious font file downloads, and endpoint protection solutions that can detect and prevent exploitation attempts. Security teams should also consider implementing monitoring for unusual font parsing activities and system crashes that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and memory safety practices, aligning with ATT&CK technique T1059.007 for process injection and T1203 for exploitation for client execution. Regular security assessments should include font file analysis and testing of parsing components to identify similar vulnerabilities in other software applications. Additionally, system administrators should ensure that all font handling processes are properly sandboxed and that privilege separation is maintained to limit the potential impact should exploitation occur.