Off-by-One Write in fontconfig Sfnt Handling Causes Code Execution

Publication date: 2026-03-25

Last updated on: 2026-03-27

Assigner: MITRE

Description

fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, and potentially a crash or code execution. This is in FcFontCapabilities in fcfreetype.c.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-03-25

Last Modified

2026-03-27

Generated

2026-07-06

AI Q&A

2026-03-25

EPSS Evaluated

2026-07-05

NVD

CVE-2026-34085

EUVD

EUVD-2026-15934

Affected Vendors & Products

Vendor	Product	Version / Range
fontconfig_project	fontconfig	to 2.17.1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-193	A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.

Attack-Flow Graph

Executive Summary

This vulnerability exists in fontconfig versions before 2.17.1. It is caused by an off-by-one error in memory allocation during the handling of sfnt capabilities in the function FcFontCapabilities within the file fcfreetype.c. This error leads to a one-byte out-of-bounds write, which can potentially cause a crash or allow code execution.

Impact Analysis

The vulnerability can lead to a one-byte out-of-bounds write, which may cause the affected application to crash or, in a worst-case scenario, allow an attacker to execute arbitrary code. This can compromise the stability and security of systems using vulnerable versions of fontconfig.

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