CVE-2026-33018
Publication date 14 April 2026
Last updated 16 April 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| libsixel | 25.10 questing |
Needs evaluation
|
| 24.04 LTS noble |
Needs evaluation
|
|
| 22.04 LTS jammy |
Needs evaluation
|
|
| 20.04 LTS focal |
Needs evaluation
|
|
| 18.04 LTS bionic |
Needs evaluation
|
|
| 16.04 LTS xenial |
Needs evaluation
|
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
7.0 · High
|
| Attack vector | Local |
| Attack complexity | High |
| Privileges required | None |
| User interaction | Required |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity impact | High |
| Availability impact | High |
| Vector | CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H |