CVE-2011-3256 in iOS
Summary
by MITRE
FreeType 2 before 2.4.7, as used in CoreGraphics in Apple iOS before 5, Mandriva Enterprise Server 5, and possibly other products, allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted font, a different vulnerability than CVE-2011-0226.
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Analysis
by VulDB Data Team • 11/24/2021
FreeType 2 version 2.4.7 and earlier contains a critical memory corruption vulnerability that affects multiple operating systems including Apple iOS versions before 5 and Mandriva Enterprise Server 5. This vulnerability stems from inadequate input validation within the font parsing mechanism, specifically when processing malformed font files. The flaw allows remote attackers to craft malicious font files that, when processed by the affected FreeType library, can trigger memory corruption conditions leading to arbitrary code execution or system crashes. The vulnerability is classified as a heap-based buffer overflow under CWE-121, where insufficient bounds checking permits data to be written beyond allocated memory regions. This type of vulnerability falls under the ATT&CK technique T1059.007 for process injection and T1068 for exploit for privilege escalation. The impact extends beyond simple denial of service as the memory corruption can be leveraged to execute malicious code with the privileges of the affected application. The vulnerability is particularly dangerous because font files are commonly encountered in normal user workflows, making exploitation trivial through email attachments, web content, or downloaded files. Attackers can craft font files that contain malicious payloads designed to overwrite critical memory structures, potentially leading to complete system compromise. The affected systems include various implementations of the CoreGraphics framework in Apple iOS, which utilizes FreeType for font rendering, as well as enterprise server environments using Mandriva Enterprise Server 5. This vulnerability demonstrates the inherent risks in font processing libraries and highlights the importance of proper input sanitization and memory management practices. The issue represents a significant security gap in font handling mechanisms and requires immediate patching of the FreeType library to prevent exploitation. Organizations should prioritize updating their FreeType implementations to version 2.4.7 or later, which contains the necessary fixes to prevent the memory corruption conditions that enable arbitrary code execution. The vulnerability also underscores the need for robust sandboxing of font processing components and input validation at multiple layers of the application stack.
The technical implementation of this vulnerability involves the improper handling of font table structures during parsing operations. When FreeType encounters malformed font data, particularly within table headers or metadata sections, the library fails to properly validate the size parameters before attempting to allocate or access memory regions. This allows attackers to manipulate the parsing logic to cause buffer overflows or memory corruption in adjacent memory locations. The vulnerability is particularly insidious because it can be triggered through legitimate font processing operations, making it difficult to detect through traditional network monitoring or application firewalls. The exploitation requires careful crafting of font files that can bypass standard security measures while still maintaining valid font structure to pass initial validation checks. The memory corruption typically manifests as stack or heap corruption that can be leveraged to redirect program execution flow. This vulnerability has been classified under multiple attack frameworks including ATT&CK's T1203 for Exploitation for Client Execution, emphasizing the client-side nature of the attack vector. The affected products represent a broad spectrum of operating systems and applications that rely on FreeType for font rendering, making the impact widespread across multiple security domains and threat models.