{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "1.8.7-r1"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "CPE_RANGE",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6d628cf43548e1f2739cbb13afcc6e8257868db5"
            }
          ],
          "repo": "https://github.com/saitoha/libsixel",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-2xgm-4x47-2x2p"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-122",
      "CWE-190"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33020.json"
  },
  "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.",
  "id": "CVE-2026-33020",
  "modified": "2026-07-15T01:48:50.036609447Z",
  "published": "2026-04-14T21:53:00.388Z",
  "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"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow"
}