CVE-2011-3439 in iOS
Summary
by MITRE
FreeType in CoreGraphics in Apple iOS before 5.0.1 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted font in a document.
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Analysis
by VulDB Data Team • 11/26/2021
The vulnerability identified as CVE-2011-3439 represents a critical memory corruption flaw within the FreeType font rendering library when integrated into Apple iOS CoreGraphics framework. This issue affects iOS versions prior to 5.0.1 and demonstrates how font processing components can serve as attack vectors for remote code execution. The vulnerability arises from insufficient input validation and memory management within the font parsing routines that handle various font formats including TrueType and OpenType. Attackers can craft malicious font files that, when processed by the vulnerable iOS system, trigger memory corruption conditions leading to arbitrary code execution or system crashes.
The technical implementation of this vulnerability stems from improper bounds checking and memory allocation handling during font file parsing operations. When iOS processes documents containing specially crafted fonts, the FreeType library fails to properly validate font structure elements such as table offsets, glyph data sizes, and font header information. This lack of validation allows attackers to manipulate memory layout through carefully constructed font files that exceed expected buffer boundaries or reference invalid memory locations. The vulnerability operates at the intersection of font processing and memory management, where insufficient sanitization of font metadata enables attackers to overwrite critical memory regions or execute code within the context of the font rendering process.
From an operational perspective, this vulnerability presents significant risk to iOS users as it enables remote code execution through seemingly benign document attachments or web content. The attack surface expands beyond traditional document processing to include any application that utilizes CoreGraphics for font rendering, potentially affecting email clients, web browsers, and document viewers. The memory corruption can manifest as either privilege escalation leading to arbitrary code execution or denial of service through system crashes that render the device unusable until reboot. This vulnerability directly impacts the iOS security model by undermining the sandboxing mechanisms that protect system resources from unauthorized access through font processing components.
The exploitation of CVE-2011-3439 aligns with ATT&CK technique T1059.007 for process injection and T1547.001 for privilege escalation through system component manipulation. This vulnerability also maps to CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds write vulnerabilities. The security implications extend beyond immediate exploitation to include potential for persistent compromise through font-based malware delivery mechanisms. Organizations and users should prioritize immediate patching of affected iOS versions to prevent exploitation, as the vulnerability does not require user interaction beyond opening documents containing malicious fonts. The remediation strategy should include monitoring for suspicious font file processing and implementing network-level controls to filter potentially malicious documents containing embedded fonts that could trigger this vulnerability.