CVE-2026-33021: high-severity vulnerability in saitoha libsixel
libsixel: Use-after-free in sixel_encoder_encode_bytes()
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.3epss 0.2%
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/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
Affected products
saitoha · libsixelRelated CVEs — saitoha libsixel
In the same product, most dangerous first.
CVE-2026-33023HIGHlibsixel: Use-after-free in load_with_gdkpixbuf()EPSS 0.3%CVE-2026-33019HIGHlibsixel: Integer overflow leads to Out-of-bounds Read in img2sixelEPSS 0.3%CVE-2025-9300MEDIUMsaitoha libsixel img2sixel encoder.c sixel_debug_print_palette stack-based overflowEPSS 0.3%CVE-2026-110601MEDIUMlibsixel before 1.8.7-r1 and 1.9.0 through 1.10.5 Heap Out-of-Bounds Write via GIFEPSS 0.2%CVE-2026-33020HIGHlibsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer OverflowEPSS 0.2%CVE-2026-33018HIGHlibsixel: Use-After-Free in load_gif()EPSS 0.2%