ubuntu-cve-2026-33018
Vulnerability from osv_ubuntu
Published
2026-04-14 22:16
Modified
2026-05-20 15:27
Summary
Details
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.
Severity
7.0 (High)
N/A (UNKNOWN)
References
{
"affected": [
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libsixel-bin",
"binary_version": "1.5.2-2"
},
{
"binary_name": "libsixel1",
"binary_version": "1.5.2-2"
}
]
},
"package": {
"ecosystem": "Ubuntu:16.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.5.2-2?arch=source\u0026distro=xenial"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.4.2-1",
"1.5.2-2"
]
},
{
"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"
}
]
},
"package": {
"ecosystem": "Ubuntu:18.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.7.3-1?arch=source\u0026distro=bionic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.5.2-2",
"1.7.3-1"
]
},
{
"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"
}
]
},
"package": {
"ecosystem": "Ubuntu:20.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.8.2-2.1?arch=source\u0026distro=focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.8.2-1",
"1.8.2-2.1"
]
},
{
"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"
}
]
},
"package": {
"ecosystem": "Ubuntu:22.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.10.3-3?arch=source\u0026distro=jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.8.6-2",
"1.10.3-2",
"1.10.3-3"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libsixel-bin",
"binary_version": "1.10.3-3build1"
},
{
"binary_name": "libsixel-examples",
"binary_version": "1.10.3-3build1"
},
{
"binary_name": "libsixel1",
"binary_version": "1.10.3-3build1"
}
]
},
"package": {
"ecosystem": "Ubuntu:24.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.10.3-3build1?arch=source\u0026distro=noble"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.3-3",
"1.10.3-3build1"
]
},
{
"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"
}
]
},
"package": {
"ecosystem": "Ubuntu:25.10",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.10.5-1?arch=source\u0026distro=questing"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.5-1"
]
},
{
"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"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "libsixel",
"purl": "pkg:deb/ubuntu/libsixel@1.10.5-1build1?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.10.5-1",
"1.10.5-1build1"
]
}
],
"aliases": [],
"details": "libsixel is a SIXEL encoder/decoder implementation derived from kmiya\u0027s 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\u0027s 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.",
"id": "UBUNTU-CVE-2026-33018",
"modified": "2026-05-20T15:27:21Z",
"published": "2026-04-14T22:16:00Z",
"references": [
{
"type": "REPORT",
"url": "https://ubuntu.com/security/CVE-2026-33018"
},
{
"type": "REPORT",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-33018"
},
{
"type": "REPORT",
"url": "https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp"
},
{
"type": "REPORT",
"url": "https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1"
}
],
"related": [],
"schema_version": "1.7.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2026-33018"
]
}
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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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