libsixel: Use-After-Free in load_gif()

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Summary

CVECVE-2026-33018
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-14 22:16:30 UTC
Updated2026-04-17 15:38:09 UTC
Descriptionlibsixel 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.

Risk And Classification

Primary CVSS: v3.1 7 HIGH from [email protected]

CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS: 0.000160000 probability, percentile 0.037700000 (date 2026-04-21)

Problem Types: CWE-416 | CWE-416 CWE-416: Use After Free

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7HIGHCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
3.1CNADECLARED7HIGHCVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Saitoha Libsixel affected < 1.8.7-rc1 Not specified

References

ReferenceSourceLinkTags
github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp [email protected] github.com
github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 [email protected] github.com
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