---
id: CVE-2026-33023
title: libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
summary: >-
  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
  cl…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
vendor: saitoha
product: libsixel
affected:
  - libsixel <= 1.8.7
published: '2026-04-14'
updated: '2026-07-25'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-33023'
references:
  - url: 'https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6
    label: security-advisories@github.com
  - url: >-
      https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00253
epssPercentile: 0.14954
ingestedAt: '2026-07-26T10:11:59.908Z'
---

## Overview

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.

## Affected

- `libsixel <= 1.8.7`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.