CVE-2017-11570 in FontForge
Summary
by MITRE
FontForge 20161012 is vulnerable to a buffer over-read in umodenc (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 buffer over-read vulnerability in the umodenc function within the parsettf.c source file that presents significant security risks to systems processing font files. This vulnerability stems from inadequate input validation when parsing OpenType font files, specifically in how the software handles malformed or crafted font data during the parsing process. The flaw occurs when the application attempts to read memory beyond the allocated buffer boundaries while processing certain font table structures, creating potential attack vectors for malicious actors to exploit.
The technical implementation of this vulnerability resides in the umodenc function which processes font modification encoding data during OpenType file parsing. When FontForge encounters a specially crafted OTF file containing malformed table structures or unexpected data sequences, the parsing logic fails to properly bounds-check memory accesses, leading to memory corruption that can result in either denial of service conditions or arbitrary code execution. This type of vulnerability falls under the CWE-125 weakness category, specifically representing an out-of-bounds read condition that can be leveraged for privilege escalation or system compromise.
The operational impact of CVE-2017-11570 extends beyond simple denial of service scenarios as it represents a potential code execution vector that could be exploited in various attack contexts. An attacker could craft a malicious OTF file designed to trigger the buffer over-read condition when opened by FontForge, potentially allowing remote code execution on systems running vulnerable versions of the software. This vulnerability is particularly concerning in environments where font processing is automated or where users regularly open font files from untrusted sources, as it could be exploited through email attachments, web downloads, or file sharing platforms.
The attack surface for this vulnerability includes any system running FontForge 20161012 that processes OpenType font files, particularly in web applications, desktop environments, or automated font conversion systems. Security practitioners should consider this vulnerability in the context of the ATT&CK framework under the T1059 technique for execution through command and scripting interpreters, as successful exploitation could enable attackers to execute arbitrary code on target systems. The vulnerability also relates to T1203, which covers legitimate programs being used for defense evasion, as the malicious font file could be used to bypass security controls that might not detect the code execution vector.
Mitigation strategies for CVE-2017-11570 primarily involve immediate software updates to versions that have patched the buffer over-read condition in the parsettf.c file. Organizations should prioritize patch management processes to ensure all instances of FontForge are updated to versions containing the fixed parsing logic. Additionally, implementing strict file validation procedures and restricting font file processing to trusted sources can help reduce the risk exposure. Network-level controls such as email filtering and web proxy configurations can also prevent potentially malicious font files from reaching end-user systems. The vulnerability demonstrates the importance of proper memory bounds checking and input validation in font processing libraries, which should be considered when implementing security controls for any font handling applications.