libsixel: libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-33021 is fixed in libsixel on 1 platform by DEBIAN-CVE-2026-33021 (version 1:1.8.7-r2-1), released April 14, 2026. It is not reported as exploited. Patch Radar priority: High.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| libsixel · Debian 14 | 1:1.8.7-r2-1 | DEBIAN-CVE-2026-33021 | Apr 14, 2026 |
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