CVE-2026-33018 libsixel: Use-After-Free in load_gif()
A use-after-free in libsixel allows attackers to cause crashes or execute code via crafted animated GIFs processed by applications using the library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-33018?
CVE-2026-33018 is a high-severity use after free vulnerability in saitoha libsixel, published on 14 Apr 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
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.
Weakness: CWE-416
Which versions are affected by CVE-2026-33018?
It affects 1 product.
Products include Saitoha Libsixel.
How do I fix CVE-2026-33018?
Upgrade to a fixed version.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-33018 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33018 exists.
Other vulnerabilities in saitoha libsixel
Sources
Also known as DEBIAN-CVE-2026-33018, GHSA-w46f-jr9f-rgvp, UBUNTU-CVE-2026-33018.