CVE-2017-11571 in FontForge
Summary
by MITRE
FontForge 20161012 is vulnerable to a stack-based buffer overflow in addnibble (parsettf.c) resulting in DoS or code execution via a crafted otf file.
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Analysis
by VulDB Data Team • 12/13/2022
FontForge version 20161012 contains a critical stack-based buffer overflow vulnerability in the addnibble function within the parsettf.c source file. This vulnerability arises when processing specially crafted open type font files that contain malformed data structures. The flaw occurs due to insufficient bounds checking during the parsing of glyph data, specifically when the application attempts to copy data into a fixed-size stack buffer without validating the input length against the buffer capacity. The vulnerability is particularly dangerous because it can be triggered through normal font processing operations when FontForge loads or manipulates font files, making it exploitable by attackers who can convince victims to open malicious font files. The buffer overflow allows an attacker to overwrite adjacent stack memory, potentially leading to arbitrary code execution or denial of service conditions. This vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which is classified under the Common Weakness Enumeration as a fundamental memory safety issue. The attack vector follows ATT&CK technique T1203 Exploitation for Client Execution, where adversaries leverage software vulnerabilities to execute malicious code on target systems. The impact of this vulnerability extends beyond simple denial of service as it represents a privilege escalation path that could allow attackers to execute arbitrary commands with the privileges of the FontForge application process. The vulnerability is particularly concerning in environments where FontForge is used for font processing in automated workflows or where users might encounter untrusted font files from unknown sources. Given that the application processes font files as part of its core functionality, any user interaction with malicious font content could trigger the exploit. The buffer overflow scenario occurs when the addnibble function receives input data that exceeds the allocated buffer size, causing memory corruption that can be leveraged to redirect program execution flow. This type of vulnerability is classified as a high-risk security issue due to its potential for remote code execution and the fact that it affects a widely used font editing tool. Organizations using FontForge should consider immediate patching or implementing additional input validation measures to prevent exploitation. The vulnerability demonstrates the importance of proper input sanitization in font processing applications and highlights the need for robust memory management practices in software that handles external data formats. The issue affects not only individual users but also organizations that rely on FontForge for font creation and modification tasks, as it could be exploited through various attack vectors including email attachments, web downloads, or file sharing platforms. Security practitioners should monitor for exploitation attempts and ensure that all FontForge installations are updated to versions that address this buffer overflow condition. The vulnerability represents a classic example of how font parsing libraries can become attack surfaces when proper bounds checking is not implemented. This flaw underscores the necessity of defensive programming practices and input validation in applications that process complex binary formats like font files. The potential for remote code execution makes this vulnerability particularly severe and warrants immediate attention from system administrators and security teams responsible for maintaining font processing environments.