# CVE-2026-33018: libsixel: Use-After-Free in load_gif()

> A use-after-free in libsixel allows attackers to cause crashes or execute code via crafted animated GIFs processed by applications using the library.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 14 Apr 2026
- **Updated:** 16 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-33018, GHSA-w46f-jr9f-rgvp, UBUNTU-CVE-2026-33018

## What is CVE-2026-33018?

CVE-2026-33018 is a high-severity use after free vulnerability in saitoha libsixel, published on 14 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a Use-After-Free vulnerability via the load_gif() function in fromgif.c, where a single sixel_frame_t object is reused across all frames of an animated GIF and gif_init_frame() unconditionally frees and reallocates frame->pixels between frames without consulting the object's reference count. Because the public API explicitly provides sixel_frame_ref() to retain a frame and sixel_frame_get_pixels() to access the raw pixel buffer, a callback following this documented usage pattern will hold a dangling pointer after the second frame is decoded, resulting in a heap use-after-free confirmed by ASAN. Any application using sixel_helper_load_image_file() with a multi-frame callback to process user-supplied animated GIFs is affected, with a reliable crash as the minimum impact and potential for code execution. This issue has been fixed in version 1.8.7-r1.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-33018?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2026-33018?

Upgrade to a fixed version.

## Is CVE-2026-33018 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33018 exists.

## Other vulnerabilities in saitoha libsixel

- [CVE-2019-19635](https://insights.sbomify.com/CVE-2019-19635/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-19636](https://insights.sbomify.com/CVE-2019-19636/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19637](https://insights.sbomify.com/CVE-2019-19637/): Integer overflow in n/a (critical 9.8)
- [CVE-2019-19638](https://insights.sbomify.com/CVE-2019-19638/): Integer overflow in n/a (critical 9.8)
- [CVE-2022-27044](https://insights.sbomify.com/CVE-2022-27044/): Memory corruption in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33018 and fix it if it is affected.

What it is: CVE-2026-33018 is a high-severity use after free vulnerability in saitoha libsixel, published on 14 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33018 exists.

Affected product: saitoha libsixel. 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-2026-33018/ (Markdown: https://insights.sbomify.com/CVE-2026-33018/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33018
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33018
- OSV: https://osv.dev/vulnerability/CVE-2026-33018

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-33018/
Summaries are generated and may contain mistakes; the official description above is the record.