CVE-2011-0226 in FreeType
Summary
by MITRE
Integer signedness error in psaux/t1decode.c in FreeType before 2.4.6, as used in CoreGraphics in Apple iOS before 4.2.9 and 4.3.x before 4.3.4 and other products, allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via a crafted Type 1 font in a PDF document, as exploited in the wild in July 2011.
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Analysis
by VulDB Data Team • 01/19/2025
The vulnerability identified as CVE-2011-0226 represents a critical integer signedness error within the FreeType font rendering library, specifically in the psaux/t1decode.c component. This flaw affects the parsing of Type 1 fonts and was particularly exploited in mobile and desktop environments through PDF document manipulation. The vulnerability exists in FreeType versions prior to 2.4.6 and impacted Apple iOS versions before 4.2.9 and 4.3.x before 4.3.4, demonstrating the widespread nature of this font processing vulnerability. The issue manifests when processing crafted Type 1 font data within PDF documents, creating a pathway for remote code execution or denial of service conditions.
The technical root cause of this vulnerability stems from improper handling of signed and unsigned integer values during the parsing of Type 1 font data structures. When FreeType processes font metrics and glyph data, it performs calculations that assume certain values are unsigned, while they may actually be signed integers. This mismatch in integer handling leads to incorrect memory allocation decisions and buffer overflow conditions. The flaw occurs specifically during the decoding process of Type 1 font data where the software incorrectly interprets the size parameters of font components, resulting in memory corruption that can be leveraged for arbitrary code execution.
The operational impact of CVE-2011-0226 extends beyond simple application crashes to encompass full remote code execution capabilities, making it a particularly dangerous vulnerability in the context of PDF document processing. Attackers could craft malicious PDF documents containing specially crafted Type 1 fonts that, when opened by vulnerable applications, would trigger the integer overflow condition. This vulnerability was actively exploited in the wild during July 2011, demonstrating its real-world threat level and the sophistication of the attacks targeting it. The exploitation typically resulted in memory corruption that could be manipulated to execute arbitrary code with the privileges of the compromised application, potentially leading to complete system compromise.
The vulnerability aligns with CWE-190, which identifies integer overflow and underflow conditions as a critical weakness in software systems. It also maps to several ATT&CK techniques including T1059 for command and scripting interpreter and T1203 for Exploitation for Client Execution, demonstrating how this vulnerability could be leveraged as part of broader attack chains. The specific exploitation pattern follows ATT&CK's T1590 for reconnaissance and T1190 for Exploit Public-Facing Application, as attackers would typically target vulnerable applications that process PDF documents and render Type 1 fonts. Organizations using affected versions of FreeType, Apple iOS, or other products incorporating this library were at significant risk, as the vulnerability could be triggered through simple document opening operations.
Mitigation strategies for CVE-2011-0226 required immediate patching of FreeType libraries to version 2.4.6 or later, which addressed the integer signedness error through proper handling of signed and unsigned integer values during font processing. Organizations should have updated their iOS devices to versions 4.2.9 or 4.3.4, respectively, and ensured all applications that process PDF documents were updated to use patched versions of FreeType. Additional defensive measures included implementing strict PDF document validation, sandboxing applications that process font data, and monitoring for suspicious font processing activities. The vulnerability highlighted the importance of proper integer handling in cryptographic and font processing libraries, leading to improved code review practices and automated testing for similar integer-related vulnerabilities in subsequent software development cycles.