CVE-2017-11568 in FontForge
Summary
by MITRE
FontForge 20161012 is vulnerable to a heap-based buffer over-read in PSCharStringToSplines (psread.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 heap-based buffer over-read vulnerability in the PSCharStringToSplines function located within the psread.c source file. This vulnerability represents a classic memory safety issue that can be exploited through maliciously crafted open type font files. The flaw occurs when the application processes PostScript charstrings within font files, specifically during the conversion of these charstrings to spline representations. The buffer over-read happens because the application fails to properly validate the bounds of memory allocations when parsing the charstring data structure, allowing an attacker to manipulate the parsing logic and access memory beyond the allocated buffer boundaries.
The technical impact of this vulnerability extends beyond simple denial of service to potentially enable remote code execution within the context of the FontForge application. When processing a specially crafted OTF file, the PSCharStringToSplines function can be forced to read memory locations that were not intended for access, potentially exposing sensitive data or allowing arbitrary code execution. This type of vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions in software applications. The vulnerability is particularly dangerous in environments where FontForge is used to process untrusted font files, as it could be exploited in web browsers, desktop applications, or automated font processing systems.
The operational impact of CVE-2017-11568 affects any system running FontForge 20161012 that processes font files from untrusted sources. Attackers can craft malicious OTF files that trigger the buffer over-read condition when FontForge attempts to parse and render the font data. This vulnerability aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' through the exploitation of software vulnerabilities. The attack surface includes web applications that use FontForge for font processing, desktop environments where users might open untrusted font files, and automated systems that batch process font collections. The vulnerability is particularly concerning because it can be exploited without user interaction once a malicious font file is encountered, making it suitable for drive-by attacks or automated exploitation campaigns.
Mitigation strategies for this vulnerability include immediate upgrading to FontForge versions that have patched this issue, as the original vulnerable version 20161012 has been superseded by more secure releases. Organizations should implement strict font file validation and sanitization processes, particularly in environments where font files are processed from external sources. Additional protective measures include deploying web application firewalls that can detect and block malicious font file uploads, implementing sandboxing techniques for font processing operations, and conducting regular security assessments of font handling components. The vulnerability demonstrates the importance of memory safety practices in font processing libraries and highlights the need for proper bounds checking in all data parsing operations. System administrators should also consider disabling font processing capabilities in applications where they are not essential, and implement network segmentation to limit the potential impact of successful exploitation attempts.