CVE-2026-23865: FreeType Buffer Overflow Vulnerability

CVE-2026-23865 Overview

An integer overflow vulnerability exists in the tt_var_load_item_variation_store function of the FreeType library. This flaw affects versions 2.13.2 and 2.13.3 and can result in an out-of-bounds read operation when parsing HVAR/VVAR/MVAR tables in OpenType variable fonts. The vulnerability has been addressed in version 2.14.2.

Critical Impact

Successful exploitation of this vulnerability could allow attackers to read memory beyond intended boundaries when processing specially crafted OpenType variable fonts, potentially leading to information disclosure or application crashes.

Affected Products

• FreeType library version 2.13.2
• FreeType library version 2.13.3

Discovery Timeline

• 2026-03-02 - CVE CVE-2026-23865 published to NVD
• 2026-03-04 - Last updated in NVD database

Technical Details for CVE-2026-23865

Vulnerability Analysis

This vulnerability is classified as CWE-125 (Out-of-bounds Read). The integer overflow occurs within the tt_var_load_item_variation_store function, which is responsible for parsing font variation data in OpenType variable fonts. When processing HVAR (Horizontal Metrics Variation), VVAR (Vertical Metrics Variation), or MVAR (Metrics Variation) tables, insufficient validation of size calculations can lead to an integer overflow condition.

The local attack vector requires user interaction, meaning an attacker must convince a victim to open a maliciously crafted font file. Once triggered, the vulnerability enables reading data outside the allocated buffer boundaries, which could expose sensitive memory contents or cause application instability.

Root Cause

The root cause lies in inadequate bounds checking during the parsing of item variation store data within OpenType variable fonts. When the tt_var_load_item_variation_store function calculates buffer sizes for variation table data, certain arithmetic operations can overflow, resulting in smaller-than-expected buffer allocations. Subsequent read operations then access memory beyond the allocated region.

Attack Vector

The attack requires local access and user interaction. An attacker must craft a malicious OpenType variable font file containing specially constructed HVAR, VVAR, or MVAR tables designed to trigger the integer overflow. When a victim opens or previews this font file using an application that relies on the vulnerable FreeType library versions, the out-of-bounds read is triggered.

The exploitation flow involves:

1. Creating a malformed OpenType variable font with manipulated variation table entries
2. Distributing the malicious font file to potential victims
3. The victim opening the font using a vulnerable FreeType-based application
4. The integer overflow triggering an out-of-bounds read during font parsing

For detailed technical information about the vulnerability mechanism, see the GitLab Commit Update that addresses this issue.

Detection Methods for CVE-2026-23865

Indicators of Compromise

• Presence of OpenType variable font files with unusually large or malformed HVAR/VVAR/MVAR table entries
• Application crashes or unexpected behavior when rendering or previewing font files
• Memory access violations or segmentation faults in applications using FreeType library

Detection Strategies

• Monitor for crashes in applications using FreeType library, particularly when processing font files
• Implement file integrity monitoring to detect potentially malicious font files in user-accessible directories
• Use memory sanitizers (ASan, MSan) in development and testing environments to detect out-of-bounds read attempts
• Deploy endpoint detection solutions capable of monitoring for anomalous font file processing behavior

Monitoring Recommendations

• Enable verbose logging for applications that process font files to capture parsing errors
• Monitor system logs for application crashes related to font rendering or FreeType operations
• Track file downloads and email attachments containing OpenType font files (.otf, .ttf)
• Implement network monitoring to detect distribution of potentially malicious font files

How to Mitigate CVE-2026-23865

Immediate Actions Required

• Update FreeType library to version 2.14.2 or later immediately
• Audit systems to identify all applications and components using vulnerable FreeType versions (2.13.2 and 2.13.3)
• Implement file filtering to block or quarantine untrusted font files until systems are patched
• Consider temporarily restricting the processing of OpenType variable fonts in high-risk environments

Patch Information

The vulnerability is fixed in FreeType version 2.14.2. Organizations should update to this version as soon as possible. The fix addresses the integer overflow condition in the tt_var_load_item_variation_store function by implementing proper bounds checking during variation table parsing.

Patch resources:

• GitLab Commit Update - Contains the specific code changes
• SourceForge Freetype 2.14.2 - Download the patched version
• Facebook Security Advisory CVE-2026-23865 - Vendor advisory
• OpenWall OSS Security Discussion - Community discussion

Workarounds

• Restrict processing of OpenType variable fonts from untrusted sources until patching is complete
• Implement application sandboxing to limit the impact of potential memory disclosure
• Use font validation tools to inspect font files before allowing them into production environments
• Consider disabling variable font support temporarily in applications where this feature is not critical

# Configuration example
# Check installed FreeType version
pkg-config --modversion freetype2

# On Debian/Ubuntu systems, update FreeType
sudo apt update && sudo apt upgrade libfreetype6

# On Red Hat/CentOS systems
sudo yum update freetype

# Verify the updated version
pkg-config --modversion freetype2