CVE-2026-33023
libsixel: Use-after-free in load_with_gdkpixbuf()
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.
INFO
Published Date :
April 14, 2026, 11:16 p.m.
Last Modified :
July 25, 2026, 11:10 a.m.
Remotely Exploit :
No
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-33023
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] |
Solution
- Update libsixel to version 1.8.7-r1 or later.
- Recompile applications using affected libsixel versions.
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-2026-33023.
| URL | Resource |
|---|---|
| https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 | Release Notes |
| https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6 | Exploit Vendor Advisory |
| https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6 | 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-2026-33023 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-2026-33023
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-2026-33023 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33023 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 del sixel de kmiya. En las versiones 1.8.7 y anteriores, cuando se compila con la opción --with-gdk-pixbuf2, existe una vulnerabilidad de uso después de liberación en load_with_gdkpixbuf() en loader.c. La ruta de limpieza libera manualmente el objeto sixel_frame_t y sus búferes internos sin consultar el recuento de referencias, a pesar de que el objeto fue creado a través del constructor con recuento de referencias sixel_frame_new() y expuesto a la devolución de llamada pública. Una devolución de llamada que llama a sixel_frame_ref(frame) para retener una referencia lógicamente válida mantendrá un puntero colgante después de que sixel_helper_load_image_file() regrese, y cualquier acceso posterior al marco o sus campos activa un uso después de liberación confirmado por AddressSanitizer. La causa raíz es una falla de consistencia entre dos estrategias de limpieza en la misma base de código: sixel_frame_unref() se usa en load_with_builtin() pero free() sin procesar se usa en load_with_gdkpixbuf(). Un atacante que suministre una imagen manipulada a cualquier aplicación compilada contra libsixel con soporte para gdk-pixbuf2 puede activar esto de manera fiable, lo que podría conducir a revelación de información, corrupción de memoria o 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-r1'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-33023', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-04-15T18:48:25.027963Z'} -
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 (including) 1.8.7 Added Reference Type GitHub, Inc.: https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 Types: Release Notes Added Reference Type CISA-ADP: https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6 Types: Exploit, Vendor Advisory Added Reference Type GitHub, Inc.: https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6 Types: Exploit, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 15, 2026
Action Type Old Value New Value Added Reference https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6 -
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. 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. Added CVSS V3.1 AV:L/AC:L/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-hr25-g2j6-qjw6