CVE-2017-11576 in FontForge
Summary
by MITRE
FontForge 20161012 does not ensure a positive size in a weight vector memcpy call in readcfftopdict (parsettf.c) resulting in DoS via a crafted otf file.
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Analysis
by VulDB Data Team • 12/13/2022
FontForge version 20161012 contains a critical vulnerability in its font parsing functionality that can lead to a denial of service condition through a specially crafted open type font file. The vulnerability exists within the readcfftopdict function in the parsettf.c source file where a memcpy operation is performed without proper validation of the size parameter in a weight vector. This flaw represents a classic buffer overflow condition that occurs when the application attempts to copy memory using an invalid or negative size value. The vulnerability specifically manifests when processing OpenType font files that contain malformed weight vector data, causing the memcpy function to attempt copying an invalid memory region which results in an application crash or termination. The technical implementation flaw stems from insufficient input validation and parameter checking within the font parsing routine, where the size parameter derived from the font file's weight vector structure is not properly validated before being used in the memory copy operation. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, though it specifically manifests as a memory corruption issue due to improper size validation. The operational impact of this vulnerability extends beyond simple denial of service as it can be exploited by malicious actors to disrupt font processing workflows in applications that rely on FontForge for font manipulation or conversion tasks. Attackers could craft malicious OTF files that, when processed by vulnerable FontForge installations, would cause the application to crash repeatedly, effectively rendering the font processing capability unusable. This vulnerability is particularly concerning in environments where FontForge is used for automated font processing or batch operations, as it could lead to complete service disruption. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, as it allows an attacker to compromise system availability through crafted input. The vulnerability affects all versions of FontForge prior to the fix release, making it a widespread concern for organizations that depend on this font editing and conversion tool. Organizations should implement immediate mitigations including updating to patched versions of FontForge, implementing input validation measures for font files, and restricting processing of untrusted font files in automated environments. Additionally, deploying network segmentation and access controls around systems that process font files can help limit the potential impact of exploitation. The vulnerability demonstrates the importance of proper input validation in font parsing libraries and highlights the need for robust error handling in complex data processing applications that handle structured binary formats.