# CVE-2026-91186: PNG decoder: a duplicate IHDR chunk after IDAT resizes the image after allocation, causing a heap out-of-bounds write


- **Severity:** High 8.4 (`CVSS:4.0/AV:L/AC:L/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-gx8f-4rpc-4fjw

## What is CVE-2026-91186?

CVE-2026-91186 is a high-severity vulnerability in Eclipse ThreadX - GUIX, published on 20 Oct 2026. 

### Official description

The PNG chunk reader has no notion of chunk ordering. It records whether an IDAT has been seen and whether a tRNS has already supplied transparency, but nothing prevents an IHDR being read a second time.

A PNG carries exactly one IHDR and it is the first chunk. A file that places a second one after IDAT rewrites the image width, height, bit depth and pixel depth *after* the decoded-data buffer has already been allocated and filled from the original values. The pass that reverses the PNG row filters then derives its own extent from the new dimensions and walks the old allocation, moving image bytes past the end of it.

The buffer is allocated by GUIX rather than supplied by the caller, so the application has no way to size it defensively. The decoder is compiled in by default.

Weakness: CWE-787 (Out-of-bounds Write), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-91186?


## How do I fix CVE-2026-91186?

No fix has been published for CVE-2026-91186 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91186 being exploited?

There is no known exploitation of CVE-2026-91186 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91186 and fix it if it is affected.

What it is: CVE-2026-91186 is a high-severity vulnerability in Eclipse ThreadX - GUIX, published on 20 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-91186 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-2026-91186/ (Markdown: https://insights.sbomify.com/CVE-2026-91186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91186
- OSV: https://osv.dev/vulnerability/CVE-2026-91186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91186/
Summaries are generated and may contain mistakes; the official description above is the record.