CVE-2015-6976 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-2015-6977, 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-2015-6976 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 file formats including TrueType, OpenType, and other embedded font types that are commonly encountered in digital documents, web content, and system resources. The flaw specifically manifests when the system processes maliciously crafted font files that contain malformed data structures or unexpected parameter values within their headers and metadata sections. This issue falls under the category of heap-based buffer overflows and memory corruption vulnerabilities, which are classified as CWE-121 and CWE-122 in the Common Weakness Enumeration catalog, representing heap-based buffer overflow and buffer overflow conditions respectively.
The technical exploitation of this vulnerability occurs when an attacker crafts a font file with carefully constructed malicious data that triggers improper memory handling within the FontParser library. When the operating system attempts to render or process such a malformed font file, typically through applications like Safari, Mail, or any system component that displays or processes font content, the parser fails to properly validate input boundaries. This leads to memory corruption that can be leveraged by attackers to execute arbitrary code with the privileges of the affected process, or alternatively cause a denial of service condition that crashes the application or system. The vulnerability demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under technique T1059 for command and scripting interpreter, where attackers can leverage system parsing functions to achieve code execution.
The operational impact of this vulnerability extends across multiple attack vectors since font files are ubiquitous in computing environments and can be encountered in various contexts including email attachments, web pages, document files, and system resources. Attackers can deliver malicious font files through phishing campaigns, compromised websites, or malicious documents that users might legitimately open, making this vulnerability particularly dangerous for enterprise environments and individual users alike. The memory corruption can manifest as either a remote code execution exploit that allows attackers to gain system control or as a denial of service that disrupts normal system operations, potentially leading to persistent service interruptions. Given that many applications and system components rely on font rendering for proper display functionality, the attack surface is extensive and includes both user-facing applications and system-level services that process font data.
Mitigation strategies for CVE-2015-6976 should prioritize immediate system updates to the patched versions of iOS 9.1 and OS X 10.11.1, which contain the necessary security patches that address the memory corruption issues in the FontParser component. Organizations should implement comprehensive patch management procedures to ensure all affected systems are updated promptly, as the vulnerability can be exploited remotely without user interaction. Additional defensive measures include implementing application sandboxing and privilege separation techniques, configuring web content filtering to block suspicious font file types, and monitoring system logs for unusual font processing activities that might indicate exploitation attempts. Network administrators should consider implementing content inspection systems that can detect and block potentially malicious font files in email attachments and web traffic. The vulnerability highlights the importance of input validation and memory safety practices in system libraries, particularly those handling untrusted data from external sources, and demonstrates the critical need for regular security assessments of core system components that process multimedia and document content.