{"id":"CVE-2026-33018","aliases":["DEBIAN-CVE-2026-33018","EUVD-2026-22740","GHSA-w46f-jr9f-rgvp","UBUNTU-CVE-2026-33018"],"status":"published","title":"libsixel: Use-After-Free in load_gif()","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-\u003epixels 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.","severity":{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00191,"percentile":0.08838,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-416"],"published":"2026-04-14T21:45:42Z","modified":"2026-10-28T02:30:46Z","fixes":[{"ecosystem":"Debian:14","package":"libsixel","fixed_in":["1:1.8.7-r2-1"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:12","package":"libsixel","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"]},{"source":"osv","ecosystem":"Debian:13","package":"libsixel","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"]},{"source":"osv","ecosystem":"Debian:14","package":"libsixel","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"]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.4.2-1","1.5.2-2"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.5.2-2","1.7.3-1"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.2-1","1.8.2-2.1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.6-2","1.10.3-2","1.10.3-3"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.3-3","1.10.3-3build1"]},{"source":"osv","ecosystem":"Ubuntu:25.10","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1build1","1:1.8.7-r2-1"]},{"source":"osv","ecosystem":"Ubuntu:26.04:LTS","package":"libsixel","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.10.5-1","1.10.5-1build1"]}],"products":[{"vendor":"saitoha","product":"libsixel"}],"references":[{"url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp","tags":["x_refsource_CONFIRM","Exploit","Vendor Advisory","advisory","report"]},{"url":"https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1","tags":["x_refsource_MISC","Release Notes","web","report"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33018.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33018","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-33018","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-33018","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-33018","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-33018","title":"libsixel: Use-After-Free in load_gif()","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-\u003epixels 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":"published","published":"2026-04-14T21:45:42.261Z","modified":"2026-04-16T13:53:25.06Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-416"],"updated_at":"2026-11-02T14:20:07.609948Z"}],"euvd":[{"id":"EUVD-2026-22740","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-\u003epixels 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":"published","published":"2026-04-14T21:45:42Z","modified":"2026-04-16T13:53:25Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T19:24:24.386229Z"}],"nvd":[{"id":"CVE-2026-33018","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-\u003epixels 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":"published","published":"2026-04-14T22:16:30.213Z","modified":"2026-07-25T10:10:00.167Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-416"],"updated_at":"2026-11-02T14:12:14.748836Z"}],"osv":[{"id":"CVE-2026-33018","title":"libsixel: Use-After-Free in load_gif()","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-\u003epixels 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":"published","published":"2026-04-14T21:45:42.261Z","modified":"2026-10-28T02:30:46.235688821Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"cwes":["CWE-416"],"updated_at":"2026-11-02T15:45:01.548715Z"},{"id":"DEBIAN-CVE-2026-33018","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-\u003epixels 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":"published","published":"2026-04-14T22:16:30.213Z","modified":"2026-10-01T03:03:10.29606075Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:45:54.587575Z"},{"id":"UBUNTU-CVE-2026-33018","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-\u003epixels 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":"published","published":"2026-04-14T22:16:00Z","modified":"2026-10-17T12:59:59.267499482Z","cvss":[{"version":"3.1","score":7,"vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T16:56:16.036833Z"}]}}