saitoha libsixel up to 1.8.6 SIXEL Encoder load_gif use after free

Summaryinfo

A vulnerability described as critical has been identified in saitoha libsixel up to 1.8.6. Affected is the function load_gif of the component SIXEL Encoder. The manipulation results in use after free. This vulnerability is reported as CVE-2026-33018. The attack can be launched remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in saitoha libsixel up to 1.8.6. Affected is the function load_gif of the component SIXEL Encoder. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-33018 since 03/17/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit.

Upgrading to version 1.8.7-rc1 eliminates this vulnerability.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• saitoha

Name

• libsixel

Version

• 1.8.0
• 1.8.1
• 1.8.2
• 1.8.3
• 1.8.4
• 1.8.5
• 1.8.6

License

• open-source

Website

• Product: https://github.com/saitoha/libsixel/

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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