{"id":"CVE-2026-33020","title":"libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel","summary":"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 si…","severity":"high","cvss":7.1,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H","cwe":["CWE-122","CWE-190"],"vendor":"saitoha","product":"libsixel","affected":["libsixel < 1.8.7-r1"],"patched":["libsixel 1.8.7-r1"],"published":"2026-04-14","updated":"2026-07-25","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-33020","references":[{"url":"https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1","label":"security-advisories@github.com"},{"url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p","label":"security-advisories@github.com"},{"url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd"],"epss":0.00205,"epssPercentile":0.10793,"ingestedAt":"2026-07-26T10:11:59.430Z","slug":"CVE-2026-33020","body":"## Overview\n\nlibsixel 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.\nThis issue has been fixed in version 1.8.7-r1.\n\n## Affected\n\n- `libsixel < 1.8.7-r1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `libsixel 1.8.7-r1`","depth":"twilight","depthScore":39,"depthScoreParts":{"impact":39.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}