{"id":"CVE-2026-33021","summary":"libsixel: Use-after-free in sixel_encoder_encode_bytes()","details":"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-\u003epixels 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.","aliases":["GHSA-j6m5-2cc7-3whc"],"modified":"2026-08-12T03:51:34.454493445Z","published":"2026-04-14T21:57:22.817Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33021.json","cna_assigner":"GitHub_M","cwe_ids":["CWE-416"]},"references":[{"type":"WEB","url":"https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33021.json"},{"type":"ADVISORY","url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-j6m5-2cc7-3whc"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33021"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/saitoha/libsixel","events":[{"introduced":"0"},{"fixed":"6d628cf43548e1f2739cbb13afcc6e8257868db5"}],"database_specific":{"source":["AFFECTED_FIELD","CPE_RANGE","REFERENCES"],"cpe":"cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*","extracted_events":[{"introduced":"0"},{"fixed":"1.8.7-r1"}]}}],"versions":["v1.8.7","nightly-latest","v1.8.6","v1.8.5","v1.8.4","v1.8.3","v1.8.2","v1.8.1","v1.8.0","v1.7.3","v1.7.2","v1.7.1","v1.6.1","v1.5.2","v1.5.1","v1.5.0","v1.4.13","v1.4.12","v1.4.11","v1.4.10","v1.4.9","v1.4.8","v1.4.7","v1.4.6","v1.4.5","v1.4.4","v1.4.3","v1.4.2","v1.4.1","v1.4.0","v1.3.6","v1.3.5","v1.3.4","v1.3.3","v1.3.2","v1.3.1","v1.1.2","v1.1.1","v1.1.0","v1.0.2","v1.0.1","v1.0.0","v0.28.0","v0.27.1","v0.27.0","v0.26.0","v0.25.5","v0.25.4","v0.25.3","v0.25.2","v0.25.1","v0.25.0","v0.24.2","v0.24.0","v0.23.2","v0.23.1","v0.23.0","v0.22.3","v0.22.2","v0.22.1","v0.22.0","v0.21.1","v0.21.0","v0.20.0","v0.19.6","v0.19.5","v0.19.4","v0.19.3","v0.19.2","v0.18.0","v0.17.2","v0.17.1","v0.17.0","v0.16.1","v0.16.0","v0.15.0","v0.14.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-33021.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H"}]}