CVE-2014-9659 in FreeType
Summary
by MITRE
cff/cf2intrp.c in the CFF CharString interpreter in FreeType before 2.5.4 proceeds with additional hints after the hint mask has been computed, which allows remote attackers to execute arbitrary code or cause a denial of service (stack-based buffer overflow) via a crafted OpenType font. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-2240.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability identified as CVE-2014-9659 represents a critical stack-based buffer overflow in the FreeType font rendering library, specifically within the CFF CharString interpreter component. This flaw affects versions of FreeType prior to 2.5.4 and stems from an incomplete remediation of a previously identified vulnerability CVE-2014-2240. The issue manifests when processing OpenType fonts that contain maliciously crafted hint mask data, creating a dangerous condition where the interpreter continues processing additional hints even after the hint mask computation has been completed. This fundamental flaw in the interpreter's control flow allows attackers to manipulate memory layout and potentially execute arbitrary code on systems that process these malformed font files.
The technical implementation of this vulnerability occurs in the cff/cf2intrp.c file where the CFF CharString interpreter handles font hinting operations. When the interpreter encounters a hint mask that has already been computed, it should terminate further hint processing to prevent overflows. However, due to the incomplete fix for CVE-2014-2240, the interpreter continues to process additional hint data beyond the computed mask boundaries, leading to stack corruption. This behavior creates a predictable overflow condition where attacker-controlled data can overwrite adjacent stack memory, potentially including return addresses and function pointers. The vulnerability operates under CWE-121, which classifies stack-based buffer overflow conditions, and demonstrates the dangerous intersection of improper input validation and incomplete security patches.
The operational impact of CVE-2014-9659 extends across multiple computing environments where FreeType is utilized for font rendering, including web browsers, desktop applications, and mobile operating systems. Attackers can leverage this vulnerability by crafting malicious OpenType fonts that, when processed by vulnerable systems, trigger the buffer overflow condition. This enables remote code execution capabilities or denial of service attacks that can crash applications or potentially escalate privileges. The vulnerability's exploitation is particularly concerning because it requires no user interaction beyond viewing content that utilizes the affected font files, making it a prime candidate for drive-by attacks. Systems using vulnerable FreeType versions are at risk when processing any OpenType font, including those embedded in PDF documents, web pages, or application resources.
Mitigation strategies for CVE-2014-9659 primarily focus on upgrading to FreeType version 2.5.4 or later, which contains the complete fix for both CVE-2014-9659 and its predecessor CVE-2014-2240. Organizations should also implement additional defensive measures including font validation controls, sandboxing of font processing operations, and network-level filtering of suspicious font content. Security teams should conduct comprehensive vulnerability assessments to identify systems running vulnerable FreeType versions and prioritize patch deployment across all affected environments. The ATT&CK framework categorizes this vulnerability under T1203, which covers exploitation for execution, and T1059, which addresses command and scripting interpreters, as attackers may leverage the vulnerability to establish persistent access through malicious font files. Organizations must also consider implementing application whitelisting policies to restrict font processing to trusted sources and reduce the attack surface for this and similar font-based vulnerabilities.