Vulnerability · Published Apr 14, 2026 · Assigned by GitHub_M
CVE-2026-33018libsixel: Use-After-Free in load_gif()
High 7.0
In plain English
A high-severity use-after-free in libsixel from saitoha. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | libsixel | no fix listed | DEBIAN-CVE-2026-33018 |
| Debian:13 | libsixel | no fix listed | DEBIAN-CVE-2026-33018 |
| Debian:14 | libsixel | 1:1.8.7-r2-1 | DEBIAN-CVE-2026-33018 |
| Ubuntu:22.04:LTS | libsixel | no fix listed | UBUNTU-CVE-2026-33018 |
| Ubuntu:24.04:LTS | libsixel | no fix listed | UBUNTU-CVE-2026-33018 |
| Ubuntu:25.10 | libsixel | no fix listed | UBUNTU-CVE-2026-33018 |
| Ubuntu:26.04:LTS | libsixel | no fix listed | UBUNTU-CVE-2026-33018 |
| Ubuntu:26.10 | libsixel | no fix listed | UBUNTU-CVE-2026-33018 |
Affected products (as reported)
Weakness: CWE-416 · Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp x_refsource_CONFIRM
- https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 x_refsource_MISC