# CVE-2026-91189: The GUIX binary resource loader never checks that a font page's glyph range is well formed.


- **Severity:** High 7.1 (`CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 20 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** GHSA-hgcj-22cg-4hfv

## What is CVE-2026-91189?

CVE-2026-91189 is a high-severity vulnerability in Eclipse ThreadX - GUIX, published on 20 Oct 2026. 

### Official description

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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-680 (Integer Overflow to Buffer Overflow), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-91189?


## How do I fix CVE-2026-91189?

No fix has been published for CVE-2026-91189 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91189 being exploited?

There is no known exploitation of CVE-2026-91189 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91189 and fix it if it is affected.

What it is: CVE-2026-91189 is a high-severity vulnerability in Eclipse ThreadX - GUIX, published on 20 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-91189 in the wild and no public exploit code.

Affected product: Eclipse ThreadX - GUIX. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-91189/ (Markdown: https://insights.sbomify.com/CVE-2026-91189/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91189
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91189
- OSV: https://osv.dev/vulnerability/CVE-2026-91189

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91189/
Summaries are generated and may contain mistakes; the official description above is the record.