CVE-2026-33021

7.3 HIGH 0.2% exploit odds Fix listed Memory safety Library

What it is

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive copy. When a resize operation is triggered, sixel_frame_convert_to_rgb888() unconditionally frees this caller-owned buffer and replaces it with a new internal allocation, leaving the caller with a dangling pointer. Any subsequent access to the original buffer by the caller constitutes a use-after-free, confirmed by AddressSanitizer. An attacker who controls incoming frames can trigger this bug repeatedly and predictably, resulting in a reliable crash with potential for code execution. This issue has been fixed in version 1.8.7-r1.

At a glance

Exploitability: Can be exploited locally on the machine without logging in. High risk of service disruption.
Exploit odds: 0.2% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-04-14 23:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-07-25 11:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.2% in the next 30 days (EPSS).
Severity: 7.3 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-04-14 23:16 UTC
Last modified: 2026-07-25 11:10 UTC
Exploit probability: 0.2% · EPSS, next 30 days
Weakness: CWE-416 · Use after free
Record status: Analyzed

Affected

Saitoha Libsixel < 1.8.7-r1

Attack profile CVSS 3.1 · 7.3

Attack vector: Local
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: Low
Availability: High

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-33021.md and follow it. Check whether this project is affected by CVE-2026-33021. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record