{
  "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-j6m5-2cc7-3whc"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-416"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33021.json"
  },
  "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.",
  "id": "CVE-2026-33021",
  "modified": "2026-08-12T03:51:34.454493445Z",
  "published": "2026-04-14T21:57:22.817Z",
  "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"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "libsixel: Use-after-free in sixel_encoder_encode_bytes()"
}