PT-2026-32951 · Libsixel · Libsixel

Nicoppida · Published 2026-04-14 · Updated 2026-04-23 · CVE-2026-33021

Positive Technologies (AI Summary)

CVSS v3.1

7.3

High

Base vector

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

Name of the Vulnerable Software and Affected Versions libsixel versions prior to 1.8.7-r1

Description A use-after-free issue exists in the sixel encoder encode bytes() function. The sixel frame init() function stores the caller-owned pixel buffer pointer directly in frame->pixels without creating a defensive copy. When a resize operation occurs, sixel frame convert to rgb888() frees this caller-owned buffer and replaces it with a new internal allocation, resulting in a dangling pointer for the caller. Subsequent access to the original buffer can lead to a crash or potential code execution. An attacker controlling incoming frames can trigger this condition repeatedly.

Recommendations Update to version 1.8.7-r1.

Fix

Use After Free

Weakness Enumeration

CWE-416

Related Identifiers

CVE-2026-33021

Affected Products

Libsixel

References · 11

• https://github.com/saitoha/libsixel/security/advisories/GHSA-j6m5-2cc7-3whc · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-33021 · Security Note
• https://security-tracker.debian.org/tracker/CVE-2026-33021 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2026-33021 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-33021 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-33021 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-33021 · Security Note
• https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 · Note
• https://twitter.com/giuseppe_1337/status/2047139721457918038 · Twitter Post
• https://twitter.com/VulmonFeeds/status/2044259463180227065 · Twitter Post
• https://twitter.com/CVEnew/status/2044338900362252369 · Twitter Post