CVE-2026-33021

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 v3 7.3 HIGH

7.3^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.5 / Impact : 4.7

Attack Vector LOCAL

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1	Release Notes
https://github.com/saitoha/libsixel/security/advisories/GHSA-j6m5-2cc7-3whc	Exploit Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-04-14 23:16

Updated : 2026-07-25 11:10

NVD link : CVE-2026-33021

Mitre link : CVE-2026-33021

CVE.ORG link : CVE-2026-33021

JSON object : View

Products Affected

saitoha

libsixel

CWE

CWE-416

Use After Free

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