CVE-2016-1775 in iOS
Summary
by MITRE
TrueTypeScaler in Apple iOS before 9.3, OS X before 10.11.4, tvOS before 9.2, and watchOS before 2.2 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 • 11/12/2024
The vulnerability identified as CVE-2016-1775 represents a critical memory corruption flaw within Apple's TrueTypeScaler component that affects multiple operating systems including iOS, macOS, tvOS, and watchOS. This vulnerability resides in the font processing subsystem that handles TrueType font rendering, making it a prime target for remote exploitation through maliciously crafted font files. The flaw manifests when the system processes specially designed font data that triggers improper memory handling during the scaling operations performed by the TrueTypeScaler engine. Attackers can leverage this vulnerability to execute arbitrary code on affected systems or cause intentional denial of service conditions that crash the targeted applications or entire operating systems. The vulnerability's impact spans across Apple's ecosystem due to the widespread use of TrueType fonts in various applications and system components, making it particularly dangerous in environments where users might encounter untrusted font content.
The technical nature of this vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions that occur when insufficient bounds checking is performed on heap-allocated memory regions. The TrueTypeScaler component likely fails to properly validate font data structures before processing them, leading to memory corruption when it attempts to scale font metrics or render glyph data. This memory corruption can be exploited through controlled input manipulation where attackers craft font files containing malformed data structures that, when processed by the vulnerable scaler, overwrite adjacent memory regions or corrupt heap metadata. The vulnerability's remote exploitability stems from the fact that font processing occurs automatically when applications display text or when system services render font content, meaning users can be compromised simply by encountering malicious font files in emails, web pages, or downloaded content. The attack vector typically involves a crafted font file that triggers the vulnerable code path when the system attempts to render or process the font, potentially leading to privilege escalation or complete system compromise depending on the execution context.
The operational impact of CVE-2016-1775 extends beyond simple denial of service scenarios to encompass full system compromise capabilities that align with ATT&CK technique T1059 for command execution and T1068 for exploit for privilege escalation. In practical deployment environments, this vulnerability creates significant risk for organizations that rely on Apple products, as the exploit can be delivered through various attack vectors including phishing emails with malicious attachments, compromised websites serving malicious font files, or even through compromised application stores. The vulnerability affects systems running Apple iOS versions prior to 9.3, macOS versions prior to 10.11.4, tvOS versions prior to 9.2, and watchOS versions prior to 2.2, representing a substantial portion of deployed Apple devices that were vulnerable to remote exploitation. Organizations must understand that the vulnerability operates at a low level within the font rendering pipeline, making it difficult to detect through traditional network monitoring or application-level security controls, as the exploitation occurs within legitimate system processes.
Mitigation strategies for CVE-2016-1775 primarily focus on immediate system updates and patches provided by Apple, which address the underlying memory corruption issues in the TrueTypeScaler implementation. System administrators should prioritize deployment of the relevant security updates for each affected platform, as Apple released patches specifically targeting this vulnerability in their respective operating system versions. Additional defensive measures include implementing strict font file validation policies, disabling automatic font rendering in untrusted environments, and employing network-based controls to prevent access to known malicious font repositories or websites. Organizations should also consider deploying application whitelisting solutions that restrict font processing to known safe font formats and versions, while monitoring for unusual font processing activities that might indicate exploitation attempts. The vulnerability's characteristics make it particularly susceptible to sandboxing controls that limit font processing capabilities, and security teams should evaluate their existing security controls to ensure proper isolation of font rendering operations from core system processes. Regular vulnerability assessments should include verification of font processing components and monitoring for any unauthorized font installations or modifications that could potentially trigger the vulnerability.