{"id":"CVE-2026-33021","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 a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffe…","severity":"high","cvss":7.3,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H","cwe":["CWE-416"],"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-2026-33021","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-j6m5-2cc7-3whc","label":"security-advisories@github.com"}],"tags":["nvd"],"epss":0.00247,"epssPercentile":0.16334,"ingestedAt":"2026-07-26T10:11:59.883Z","slug":"CVE-2026-33021","body":"## Overview\n\nlibsixel 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.\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":40,"depthScoreParts":{"impact":40.2,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}