# CVE-2026-33023: libsixel: Use-after-free in load_with_gdkpixbuf()

> A use-after-free in libsixel's gdk-pixbuf2 loader allows attackers to trigger memory corruption or code execution via crafted images.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/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:** 15 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-33023, GHSA-hr25-g2j6-qjw6, UBUNTU-CVE-2026-33023

## What is CVE-2026-33023?

CVE-2026-33023 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. In versions 1.8.7 and prior, when built with the --with-gdk-pixbuf2 option, a use-after-free vulnerability exists in load_with_gdkpixbuf() in loader.c. The cleanup path manually frees the sixel_frame_t object and its internal buffers without consulting the reference count, even though the object was created via the refcounted constructor sixel_frame_new() and exposed to the public callback. A callback that calls sixel_frame_ref(frame) to retain a logically valid reference will hold a dangling pointer after sixel_helper_load_image_file() returns, and any subsequent access to the frame or its fields triggers a use-after-free confirmed by AddressSanitizer. The root cause is a consistency failure between two cleanup strategies in the same codebase: sixel_frame_unref() is used in load_with_builtin() but raw free() is used in load_with_gdkpixbuf(). An attacker supplying a crafted image to any application built against libsixel with gdk-pixbuf2 support can trigger this reliably, potentially leading to information disclosure, memory corruption, or 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-2026-33023?

It affects 1 product.


Products: Saitoha Libsixel.

## How do I fix CVE-2026-33023?

Upgrade to a fixed version.

## Is CVE-2026-33023 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33023 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-2026-33023 and fix it if it is affected.

What it is: CVE-2026-33023 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-2026-33023 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-2026-33023/ (Markdown: https://insights.sbomify.com/CVE-2026-33023/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33023
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33023
- OSV: https://osv.dev/vulnerability/CVE-2026-33023

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33023/
Summaries are generated and may contain mistakes; the official description above is the record.