libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow_CVE-2026-33020

{
    "lastseen": "",
    "description": "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.",
    "published": "2026-04-14T21:53:00.388Z",
    "modified": "2026-04-14T21:53:00.388Z",
    "type": "cve",
    "title": "libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow",
    "source": "GitHub_M",
    "references": "https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p\nhttps://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1",
    "id": "CVE-2026-33020",
    "bulletinFamily": "",
    "cwe": [
        "CWE-122",
        "CWE-190"
    ],
    "cvelist": null,
    "sourceData": "saitoha libsixel < 1.8.7-r1",
    "sourceHref": "",
    "cvss": {
        "score": 7.1,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "libsixel",
    "version": "< 1.8.7-r1",
    "vendor": "saitoha",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}