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Fencer Vulns
high 7.0

CVE-2026-33018 json

libsixel: Use-After-Free in load_gif()

published 2026-04-14 6 mo ago modified 2026-07-25 3 mo ago also EUVD-2026-22740

cvss
7.0
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits
0
none known

Summary

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.

Patch / fix

  • libsixel_project libsixel 1.8.7-rc1
  • saitoha libsixel 1.8.7-rc1
  • libsixel Debian 14 1:1.8.7-r2-1

debian advisories DEBIAN-CVE-2026-33018

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33018 updated cvss 7.0

libsixel: libsixel: Arbitrary code execution via Use-After-Free in GIF processing

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
6 mo ago

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/saitoha/libsixel/security/advisories/GHSA-w46f-jr9f-rgvp referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.0 CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

  • saitoha libsixel

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.