---
id: "CVE-2026-91189"
kind: "vulnerability"
aliases: ["CVE-2026-91189"]
title: "GUIX font loader: malformed glyph range causes heap overflow"
severity: "high"
cvss: 7.1
epss: null
exploited: false
status: "open"
category: "other"
products: [{"name": "GUIX (Eclipse ThreadX)", "fixed": ["6.5.2.202603"], "affected": "<= 6.5.1.202602a", "ecosystem": "vendor"}]
ecosystems: []
tags: ["32-bit", "eclipse-threadx", "embedded", "font-loading", "guix", "mcu", "other"]
not_affected_if: ["64-bit-build", "no-binary-resources", "no-extended-unicode", "trusted-resources-only"]
published_at: "2026-10-20T15:17:36+00:00"
first_seen_at: "2026-10-23T21:57:20+00:00"
updated_at: "2026-10-25T03:36:12+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-91189", "first_seen_at": "2026-10-23T21:57:20+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-25T03:36:12+00:00"}]
---

# GUIX font loader: malformed glyph range causes heap overflow

The GUIX binary resource loader reads a font page's first and last glyph values without checking that the range is valid. A crafted file with first_glyph greater than last_glyph makes the buffer size calculation wrap, so the loader writes attacker-chosen glyph data past a too-small buffer.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:GUIX (Eclipse ThreadX) affected <= 6.5.1.202602a fixed 6.5.2.202603

## How to check

Check your GUIX version (version macros in gx_api.h, or your vendored copy): <= 6.5.1.202602a is affected. Then check for GX_EXTENDED_UNICODE_SUPPORT in your build flags and whether GX_BINARY_RESOURCE_SUPPORT is left enabled (default on) and your code calls gx_binres_theme_load or gx_binres_font_load on files you did not produce.

## Fix

Upgrade GUIX to 6.5.2.202603 (rejects first_glyph > last_glyph, checks reservation multiplies). Also move to the _ext loaders that take the resource length; the length-less loaders are deprecated. Workaround until then: load binary resources only from trusted sources, or build with GX_DISABLE_BINARY_RESOURCE_SUPPORT if unused.

## Timeline

- 2026-10-23T21:57:20+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-91189
- 2026-10-25T03:36:12+00:00 analyst — Read GHSA-hgcj-22cg-4hfv and 6.5.2.202603 release notes (maintainer). Affected <= 6.5.1.202602a, fixed 6.5.2.202603. No exploitation or public PoC link seen; reporter demonstrated a 303-byte theme file hijacking a function pointer (not public). Skipped social search (niche embedded).

## Documents

- [advisory] GHSA-hgcj-22cg-4hfv GUIX binary resource loader glyph range https://github.com/eclipse-threadx/guix/security/advisories/GHSA-hgcj-22cg-4hfv
- [fix] GUIX release 6.5.2.202603 notes https://github.com/eclipse-threadx/guix/releases

## From the sources

The GUIX binary resource loader never checks that a font page's glyph range is well formed. `gx_page_header_first_glyph` and `gx_page_header_last_glyph` are read verbatim from the file and only the upper bound of `last_glyph` is validated, so a page declaring `first_glyph > last_glyph` makes `last - first + 1` underflow to a very large unsigned count.



That count is multiplied by a glyph record size to reserve the load buffer, and the multiply is unchecked, so it wraps to a small value and the loader allocates a buffer far smaller than the data it is about to write. The load pass then recomputes the count in a narrower type and writes attacker-controlled glyph records into the undersized buffer.

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