CVE-2026-33020High· 7.1▾ Twilightlibsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation si…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 39.1 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Aug 4.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
0.2% → 0.2%
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.
libsixel < 1.8.7-r1Upgrade past the affected range:
libsixel 1.8.7-r1Connected by shared product, vendor, weakness, or advisory.
CVE-2026-110601Medium· 6.3libsixel before 1.8.7-r1 and 1.9.0 through 1.10.5 contains a heap out-of-bounds write vulnerability in gif_init_frame() in src/fromgif.c, which never checks the GIF transparent color index against the palette size
CVE-2026-33023High· 7.8libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
CVE-2026-33021High· 7.3libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel
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