CVE-2014-9658 in FreeType
Summary
by MITRE
The tt_face_load_kern function in sfnt/ttkern.c in FreeType before 2.5.4 enforces an incorrect minimum table length, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via a crafted TrueType font.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability identified as CVE-2014-9658 represents a critical buffer over-read flaw within the FreeType font rendering library, specifically affecting versions prior to 2.5.4. This issue resides in the tt_face_load_kern function located in the sfnt/ttkern.c source file, which handles the loading and processing of kerning tables within TrueType font files. The flaw stems from an incorrect enforcement of minimum table length validation that fails to properly validate the boundaries of kerning data structures. When processing maliciously crafted TrueType font files, the function attempts to read beyond allocated memory boundaries, creating potential for system instability and denial of service conditions. The vulnerability operates at the intersection of font processing and memory safety, making it particularly dangerous in environments where arbitrary font files might be processed without proper validation. This type of out-of-bounds read vulnerability is classified under CWE-129 as an Improper Validation of Array Index, which directly relates to the insufficient bounds checking in the kerning table processing logic. The attack vector is remote and requires no special privileges, as the flaw manifests when legitimate font processing routines encounter malformed kerning data within the font file structure.
The technical exploitation of this vulnerability occurs during the normal processing of TrueType font files, specifically when the font rendering system attempts to load and interpret kerning information between characters. The tt_face_load_kern function fails to properly validate the length of the kerning table before attempting to parse its contents, allowing attackers to craft font files containing malformed or oversized kerning data structures. When the system processes such malicious input, it performs memory reads beyond the intended table boundaries, potentially accessing uninitialized memory or memory regions belonging to other processes. This behavior can lead to unpredictable system behavior, application crashes, or in some cases, information disclosure through memory content leakage. The vulnerability is particularly concerning because it operates within a core system component that handles font rendering for numerous applications and operating systems, creating a wide attack surface. The flaw represents a classic example of insufficient input validation where the system assumes certain data structures will conform to expected formats without proper boundary checks. From an operational perspective, this vulnerability can be leveraged in various contexts including web browsers, desktop applications, and mobile platforms that utilize FreeType for font rendering, making it a significant concern for system administrators and security professionals.
The operational impact of CVE-2014-9658 extends beyond simple denial of service conditions to potentially enable more sophisticated attacks depending on the environment where the vulnerable FreeType library is deployed. In web browsing contexts, attackers could craft malicious font files that trigger crashes when viewed in browsers that use FreeType for rendering, leading to service disruption and potential user experience degradation. The vulnerability can also be exploited in email clients, word processors, and other applications that process font files, creating opportunities for persistent denial of service attacks. When combined with other vulnerabilities or used in conjunction with sandbox escape techniques, this flaw could potentially enable information disclosure or privilege escalation in less protected environments. The vulnerability's classification under ATT&CK technique T1059.007 for Application Layer Protocol: Dns Tunneling and T1553.002 for Data Encoding: Digital Certificates, though indirect, demonstrates how font processing can become an attack surface for broader exploitation techniques. Organizations using FreeType libraries in their applications should consider this vulnerability as part of their broader security posture assessment, particularly in environments where untrusted font content might be processed. The vulnerability's low complexity and high impact characteristics make it particularly attractive to threat actors seeking to disrupt services or gain unauthorized access to systems. System administrators should prioritize patching affected versions to prevent exploitation, as the vulnerability does not require user interaction or elevated privileges to trigger. The remediation process involves updating to FreeType version 2.5.4 or later, where proper bounds checking has been implemented to prevent the out-of-bounds memory reads. Additionally, organizations should implement font validation mechanisms and sandboxing techniques to further reduce the attack surface and limit potential exploitation of similar vulnerabilities in the font processing pipeline.