{"id":"DEBIAN-CVE-2026-33023","details":"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.","modified":"2026-09-14T17:03:08.071511060Z","published":"2026-04-14T23:16:27.820Z","upstream":["CVE-2026-33023"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-33023"}],"affected":[{"package":{"name":"libsixel","ecosystem":"Debian:12","purl":"pkg:deb/debian/libsixel?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.3-3","1.10.5-1","1:1.8.7-1","1:1.8.7-2","1:1.8.7-3","1:1.8.7-4","1:1.8.7-5","1:1.8.7-6","1:1.8.7-r2-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Debian:13","purl":"pkg:deb/debian/libsixel?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1","1:1.8.7-1","1:1.8.7-2","1:1.8.7-3","1:1.8.7-4","1:1.8.7-5","1:1.8.7-6","1:1.8.7-r2-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Debian:14","purl":"pkg:deb/debian/libsixel?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1:1.8.7-r2-1"}]}],"versions":["1.10.5-1","1:1.8.7-1","1:1.8.7-2","1:1.8.7-3","1:1.8.7-4","1:1.8.7-5","1:1.8.7-6"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33023.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"}]}