{"id":"CVE-2026-33020","summary":"libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow","details":"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.\nThis issue has been fixed in version 1.8.7-r1.","aliases":["GHSA-2xgm-4x47-2x2p"],"modified":"2026-07-15T01:48:50.036609447Z","published":"2026-04-14T21:53:00.388Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33020.json","cna_assigner":"GitHub_M","cwe_ids":["CWE-122","CWE-190"]},"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-2026-33020.json"},{"type":"ADVISORY","url":"https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33020"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/saitoha/libsixel","events":[{"introduced":"0"},{"fixed":"6d628cf43548e1f2739cbb13afcc6e8257868db5"}],"database_specific":{"cpe":"cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*","extracted_events":[{"introduced":"0"},{"fixed":"1.8.7-r1"}],"source":["AFFECTED_FIELD","CPE_RANGE","REFERENCES"]}}],"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-2026-33020.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H"}]}