CVE-2026-33023 libsixel: Use-after-free in load_with_gdkpixbuf()
A use-after-free in libsixel's gdk-pixbuf2 loader allows attackers to trigger memory corruption or code execution via crafted images.
- 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-2026-33023?
CVE-2026-33023 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. In versions 1.8.7 and prior, when built with the --with-gdk-pixbuf2 option, a use-after-free vulnerability exists in load_with_gdkpixbuf() in loader.c. The cleanup path manually frees the sixel_frame_t object and its internal buffers without consulting the reference count, even though the object was created via the refcounted constructor sixel_frame_new() and exposed to the public callback. A callback that calls sixel_frame_ref(frame) to retain a logically valid reference will hold a dangling pointer after sixel_helper_load_image_file() returns, and any subsequent access to the frame or its fields triggers a use-after-free confirmed by AddressSanitizer. The root cause is a consistency failure between two cleanup strategies in the same codebase: sixel_frame_unref() is used in load_with_builtin() but raw free() is used in load_with_gdkpixbuf(). An attacker supplying a crafted image to any application built against libsixel with gdk-pixbuf2 support can trigger this reliably, potentially leading to information disclosure, memory corruption, or code execution. This issue has been fixed in version 1.8.7-r1.
Weakness: CWE-416
Which versions are affected by CVE-2026-33023?
It affects 1 product.
Products include Saitoha Libsixel.
How do I fix CVE-2026-33023?
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-2026-33023 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33023 exists.
Other vulnerabilities in saitoha libsixel
Sources
Also known as DEBIAN-CVE-2026-33023, GHSA-hr25-g2j6-qjw6, UBUNTU-CVE-2026-33023.