Vulnerability 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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Saitoha | Libsixel | < 1.8.7-r1 |
Related Weaknesses (CWE)
References
- https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1Release Notes
- https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvpExploitVendor Advisory
FAQ
What is CVE-2026-33018?
CVE-2026-33018 is a vulnerability with a CVSS score of 7.0 (HIGH). 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 ...
How severe is CVE-2026-33018?
CVE-2026-33018 has been rated HIGH with a CVSS base score of 7.0/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-33018?
Check the references section above for vendor advisories and patch information. Affected products include: Saitoha Libsixel.