CVE-2015-9383 in FreeType
Summary
by MITRE
FreeType before 2.6.2 has a heap-based buffer over-read in tt_cmap14_validate in sfnt/ttcmap.c.
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Analysis
by VulDB Data Team • 12/11/2023
The vulnerability identified as CVE-2015-9383 represents a critical heap-based buffer over-read flaw within the FreeType font rendering library version 2.6.1 and earlier. This issue resides in the tt_cmap14_validate function located within the sfnt/ttcmap.c source file, which is responsible for validating Unicode character mapping tables in TrueType fonts. The flaw manifests when processing malformed or specially crafted font files that contain invalid cmap table structures, specifically affecting the cmap format 14 implementation that handles Unicode variation selectors and complex character mappings.
The technical nature of this vulnerability stems from insufficient bounds checking during the validation process of Unicode variation selector data within font files. When FreeType encounters a malformed cmap14 table structure, the validation function fails to properly verify array boundaries before accessing memory locations, leading to a buffer over-read condition. This occurs because the function assumes certain data structures maintain expected sizes and formats without adequate verification of input parameters. The over-read allows an attacker to potentially access uninitialized memory regions, which could contain sensitive data from other parts of the application's memory space, including cryptographic keys, session tokens, or other confidential information.
The operational impact of this vulnerability extends beyond simple memory access violations, as it can be exploited in various attack scenarios including remote code execution, information disclosure, and denial of service conditions. Attackers can craft malicious font files that trigger the buffer over-read when processed by applications using FreeType, such as web browsers, document viewers, or any software that renders TrueType fonts. The vulnerability is particularly concerning because it can be exploited through common attack vectors such as web browsing, email attachments, or document processing, making it a significant risk for end users and system administrators. This flaw affects a wide range of applications that depend on FreeType for font rendering, including popular web browsers like Chrome, Firefox, and Safari, as well as various office suites and desktop environments.
Mitigation strategies for this vulnerability primarily focus on immediate software updates and patches to FreeType version 2.6.2 or later, which contain the necessary fixes to properly validate cmap14 table structures and prevent the buffer over-read condition. System administrators should prioritize patching affected applications that utilize FreeType, particularly web browsers, document processors, and any font rendering services. Additional protective measures include implementing strict input validation for font files in applications, deploying web application firewalls, and utilizing sandboxing techniques to limit the potential impact of exploitation. Security monitoring should focus on detecting unusual font processing activities and memory access patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and could be categorized under ATT&CK technique T1059 for execution through font rendering processes, highlighting the need for comprehensive security controls across multiple attack surfaces.