CVE-2026-33021 Details
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.
A use-after-free vulnerability has been identified in libsixel, a SIXEL encoder/decoder library, in versions through 1.8.7. The issue arises in the function 'sixel_encoder_encode_bytes()', where the pixel buffer pointer provided by the caller is stored directly in the frame structure without a defensive copy. This oversight allows the buffer to be freed during a resize operation, leaving a dangling pointer. Subsequent access to this buffer by the caller results in a use-after-free condition, which has been confirmed using AddressSanitizer. This vulnerability can be exploited to cause a crash and potentially execute arbitrary code.
Users should upgrade to libsixel version 1.8.7-r1, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Apr 16, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1 | [email protected] | Release Notes |
| https://github.com/saitoha/libsixel/security/advisories/GHSA-j6m5-2cc7-3whc | [email protected] | ExploitVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-416 | Use After Free | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| saitoha libsixel | < 1.8.7-r1 |
CPE
Remediation
| |
Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 25, 2026 | CVE Translated | [email protected] |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Apr 23, 2026 | Initial Analysis | [email protected] |
| Apr 14, 2026 | New CVE Received | [email protected] |