{"id":"UBUNTU-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":"2026-05-20T16:12:44.557977148Z","published":"2026-04-14T23:16:00Z","upstream":["CVE-2026-33023"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-33023"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-33023"},{"type":"REPORT","url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6"},{"type":"REPORT","url":"https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1"}],"affected":[{"package":{"name":"libsixel","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.2-1","1.5.2-2"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.5.2-2"},{"binary_name":"libsixel1","binary_version":"1.5.2-2"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:18.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=bionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.2-2","1.7.3-1"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.7.3-1"},{"binary_name":"libsixel-examples","binary_version":"1.7.3-1"},{"binary_name":"libsixel1","binary_version":"1.7.3-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:20.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=focal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.2-1","1.8.2-2.1"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.8.2-2.1"},{"binary_name":"libsixel-examples","binary_version":"1.8.2-2.1"},{"binary_name":"libsixel1","binary_version":"1.8.2-2.1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:22.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=jammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.6-2","1.10.3-2","1.10.3-3"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.10.3-3"},{"binary_name":"libsixel-examples","binary_version":"1.10.3-3"},{"binary_name":"libsixel1","binary_version":"1.10.3-3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.3-3","1.10.3-3build1"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.10.3-3build1"},{"binary_name":"libsixel-examples","binary_version":"1.10.3-3build1"},{"binary_name":"libsixel1","binary_version":"1.10.3-3build1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.10.5-1"},{"binary_name":"libsixel-examples","binary_version":"1.10.5-1"},{"binary_name":"libsixel1","binary_version":"1.10.5-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}},{"package":{"name":"libsixel","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/libsixel?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1","1.10.5-1build1"],"ecosystem_specific":{"binaries":[{"binary_name":"libsixel-bin","binary_version":"1.10.5-1build1"},{"binary_name":"libsixel-examples","binary_version":"1.10.5-1build1"},{"binary_name":"libsixel1","binary_version":"1.10.5-1build1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-33023.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"},{"type":"Ubuntu","score":"medium"}]}