libsixel: Use-after-free in load_with_gdkpixbuf()

{
  "id": "f36375b7267d9f782954ba145c428d49bb27042e753ca0d8f9c1837931d4a86f",
  "url": "https://osv.dev/vulnerability/CVE-2026-33023",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "libsixel: Use-after-free in load_with_gdkpixbuf()",
    "summary": "libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. In versions 1.8.7 and prior, when built with the --with-gdk-pixbuf2 option, a use-after-free vulnerability exists in load_with_gdkpixbuf() in loader.c. The cleanup path manually frees the sixel_frame_t object and its internal buffers without consulting the reference count, even though the object was created via the refcounted constructor sixel_frame_new() and exposed to the public callback. A callback that calls sixel_frame_ref(frame) to retain a logically valid reference will hold a dangling pointer after sixel_helper_load_image_file() returns, and any subsequent access to the frame or its fields triggers a use-after-free confirmed by AddressSanitizer. The root cause is a consistency failure between two cleanup strategies in the same codebase: sixel_frame_unref() is used in load_with_builtin() but raw free() is used in load_with_gdkpixbuf(). An attacker supplying a crafted image to any application built against libsixel with gdk-pixbuf2 support can trigger this reliably, potentially leading to information disclosure, memory corruption, or code execution. This issue has been fixed in version 1.8.7-r1.",
    "evidence": "osv:CVE-2026-33023",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-33023",
      "aliases": [
        "CVE-2026-33023",
        "GHSA-hr25-g2j6-qjw6"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/saitoha/libsixel",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "6d628cf43548e1f2739cbb13afcc6e8257868db5"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "1.8.7"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "6d628cf43548e1f2739cbb13afcc6e8257868db5"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v1.8.7-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-2026-33023.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:31.304887944Z",
      "provider": "osv",
      "references": [
        "https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33023.json",
        "https://github.com/saitoha/libsixel/security/advisories/GHSA-hr25-g2j6-qjw6",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-33023"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-416"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33023.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-33023",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 497961,
  "published_at": "2026-04-14T22:05:31.493+00:00"
}