CVE-2026-33018
libsixel: Use-After-Free in load_gif()
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.
INFO
Published Date :
April 14, 2026, 10:16 p.m.
Last Modified :
July 25, 2026, 10:10 a.m.
Remotely Exploit :
No
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-33018
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Update to version 1.8.7-r1 or later.
- Review image processing code for safe frame handling.
- Avoid processing multi-frame animated GIFs if unable to update.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33018.
| URL | Resource |
|---|---|
| https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 | Release Notes |
| https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp | Exploit Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33018 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33018
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33018 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33018 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Translated by [email protected]
Jul. 25, 2026
Action Type Old Value New Value Added Translation Title: libsixel de saitoha, Description: libsixel es una implementación de codificador/decodificador SIXEL derivada de sixel de kmiya. Las versiones 1.8.7 y anteriores contienen una vulnerabilidad de uso después de liberación a través de la función load_gif() en fromgif.c, donde un único objeto sixel_frame_t se reutiliza en todos los fotogramas de un GIF animado y gif_init_frame() libera y reasigna incondicionalmente frame -> pixels entre fotogramas sin consultar el contador de referencias del objeto. Debido a que la API pública proporciona explícitamente sixel_frame_ref() para retener un fotograma y sixel_frame_get_pixels() para acceder al búfer de píxeles sin procesar, una devolución de llamada que siga este patrón de uso documentado mantendrá un puntero colgante después de que se decodifique el segundo fotograma, lo que resultará en un uso después de liberación en el heap confirmado por ASAN. Cualquier aplicación que utilice sixel_helper_load_image_file() con una devolución de llamada multifotograma para procesar GIFs animados proporcionados por el usuario se ve afectada, con un bloqueo fiable como el impacto mínimo y potencial de ejecución de código. Este problema ha sido solucionado en la versión 1.8.7-r1. -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'saitoha', 'product': 'libsixel', 'versions': [{'status': 'affected', 'version': '< 1.8.7-rc1'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-33018', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-04-16T13:52:34.921283Z'} -
Initial Analysis by [email protected]
Apr. 23, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:* versions up to (excluding) 1.8.7-r1 Added Reference Type GitHub, Inc.: https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 Types: Release Notes Added Reference Type GitHub, Inc.: https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp Types: Exploit, Vendor Advisory -
New CVE Received by [email protected]
Apr. 14, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H Added CWE CWE-416 Added Reference https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 Added Reference https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp