CVE-2017-11575 in FontForge
Summary
by MITRE
FontForge 20161012 is vulnerable to a buffer over-read in strnmatch (char.c) resulting in DoS or code execution via a crafted otf file, related to a call from the readttfcopyrights function in parsettf.c.
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Analysis
by VulDB Data Team • 12/13/2022
FontForge version 20161012 contains a critical buffer over-read vulnerability in the strnmatch function located within the char.c source file. This flaw represents a classic memory safety issue that can be exploited through maliciously crafted OpenType font files, specifically targeting the readttfcopyrights function in parsettf.c. The vulnerability occurs when the application processes font files containing specially constructed data that triggers an out-of-bounds memory read operation. The buffer over-read condition arises because the strnmatch function fails to properly validate the length of input strings before performing memory comparisons, allowing an attacker to manipulate the program flow through carefully crafted font metadata.
The technical exploitation of this vulnerability can result in either denial of service or arbitrary code execution depending on the specific memory layout and execution environment. When an attacker submits a malicious otf file, the readttfcopyrights function processes the font's copyright information and inadvertently triggers the buffer over-read in strnmatch. This condition can lead to program crashes, memory corruption, or potentially allow remote code execution if the attacker can control the memory contents being read. The vulnerability is particularly dangerous because it operates at the parsing layer of font processing, making it accessible through normal font rendering operations that many applications perform automatically.
The operational impact of this vulnerability extends across various systems that utilize FontForge for font processing, including graphic design applications, web browsers that render fonts, and desktop publishing software. The attack vector requires only the delivery of a malicious font file, making it particularly effective for phishing campaigns, malware distribution, or remote exploitation in web environments. This vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and demonstrates how font parsing libraries can become attack surfaces for privilege escalation or system compromise. The issue affects not just FontForge directly but also any software that relies on its font processing capabilities or similar parsing functions.
Mitigation strategies for this vulnerability include immediate patching of FontForge to version 20170731 or later, which contains the necessary fixes for the buffer over-read condition. Organizations should implement strict font file validation and sanitization procedures, particularly for files received from untrusted sources. Security measures should include sandboxing font processing operations, implementing input length validation, and monitoring for unusual memory access patterns during font parsing. Additionally, administrators should consider disabling automatic font rendering in web browsers and email clients when processing untrusted content, as recommended by the mitre ATT&CK framework for mitigating font-based attacks. Regular security updates and vulnerability assessments should be conducted to ensure that font processing libraries remain secure against similar memory safety issues.