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CVE-2026-33021

Saitoha Libsixel use-after-free

7.3 HIGHPublic exploitEPSS 0.21%
  1. Published14 Apr 2026

Description

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.

CVSS 3.1 breakdown

Attack vectorLocal
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityLow
IntegrityLow
AvailabilityHigh
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Affected products

Saitoha Libsixel< 1.8.7-r1

Remediation

Fixed in
Saitoha Libsixel≥ 1.8.7-r1

References

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Frequently asked

Is CVE-2026-33021 being actively exploited?

CVE-2026-33021 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.21%.

How severe is CVE-2026-33021?

CVE-2026-33021 has a CVSS 3.1 base score of 7.3, rated high. EPSS estimates a 0.21% probability of exploitation.

Which products are affected by CVE-2026-33021?

Affected products include Saitoha Libsixel.

How do I fix CVE-2026-33021?

Upgrade affected software to a fixed version, for example Saitoha Libsixel 1.8.7-r1 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33021 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.