CVE-2015-5927 in Mac OS X
Summary
by MITRE
FontParser in Apple iOS before 9.1, OS X before 10.11.1, and watchOS before 2.0.1 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-2015-5942.
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Analysis
by VulDB Data Team • 11/19/2024
The vulnerability identified as CVE-2015-5927 represents a critical memory corruption flaw within Apple's FontParser component that affected multiple operating systems including iOS versions prior to 9.1, macOS versions before 10.11.1, and watchOS versions before 2.0.1. This vulnerability stems from insufficient input validation and memory management practices when processing specially crafted font files, creating a pathway for remote attackers to potentially execute arbitrary code or induce system crashes through denial of service conditions. The flaw specifically impacts the parsing mechanism responsible for handling font data structures, making it a prime target for exploitation in scenarios where users might encounter maliciously formatted font files through various attack vectors such as email attachments, web downloads, or malicious websites. The vulnerability is categorized under CWE-125 as an out-of-bounds read condition, which occurs when the FontParser attempts to access memory locations beyond the allocated buffer boundaries during font file processing, leading to unpredictable behavior and potential code execution.
The technical implementation of this vulnerability involves the improper handling of font file structures where the parser fails to properly validate the size and content of font data elements before attempting to read or process them. When encountering malformed font files containing oversized or malformed data structures, the parser's memory management routines become compromised, resulting in memory corruption that can be leveraged by attackers to manipulate program execution flow. The attack surface is particularly concerning as font files are commonly encountered in various contexts including web browsing, document viewing, and system rendering operations, making the exploitation potential widespread and difficult to prevent entirely through traditional network filtering measures. This vulnerability demonstrates a classic buffer overflow pattern where insufficient bounds checking allows attackers to overwrite adjacent memory locations, potentially leading to privilege escalation or complete system compromise.
The operational impact of CVE-2015-5927 extends beyond simple denial of service conditions to encompass serious security implications including remote code execution capabilities that could enable attackers to gain unauthorized access to affected systems. The vulnerability's remote exploitability means that attackers do not require physical access or local privileges to carry out successful attacks, making it particularly dangerous in enterprise environments where users may inadvertently encounter malicious font files through legitimate business operations. The memory corruption aspect creates instability that can be exploited to bypass security mitigations such as address space layout randomization and data execution prevention mechanisms, potentially allowing attackers to execute malicious code with system privileges. This vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1547.001 for registry run keys / startup folder, as successful exploitation could enable attackers to establish persistence mechanisms within affected systems.
Mitigation strategies for CVE-2015-5927 primarily focus on applying the official security patches released by Apple, which address the underlying memory handling issues in the FontParser component through enhanced input validation and proper bounds checking mechanisms. Organizations should prioritize immediate deployment of the relevant software updates across all affected operating systems, as the vulnerability remains exploitable in unpatched environments. Network administrators should implement additional monitoring and filtering measures to detect and block suspicious font file downloads, particularly in environments where users have access to untrusted web content or email systems. The vulnerability's classification as a memory corruption issue emphasizes the importance of maintaining up-to-date system security configurations and implementing robust application sandboxing practices to limit the potential impact of successful exploitation attempts. Regular security assessments should include verification of font handling components and monitoring for unusual system behavior that might indicate exploitation attempts.