{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "last_affected": "3.6.1rel"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "13b3d4204dd12d93d426f2157b157b149edc29bf"
            }
          ],
          "repo": "https://github.com/sumatrapdfreader/sumatrapdf",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-m423-rp8p-whj8"
  ],
  "database_specific": {
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
      "CWE-119",
      "CWE-787"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55586.json"
  },
  "details": "SumatraPDF is a multi-format reader for Windows. In 3.6.1 and earlier, a crafted CHM file can supply malformed LZX Huffman code lengths to make_decode_table in ext/CHMLib/lzx.c. In the long-code branch, the function writes new internal nodes through next_symbol before validating that the canonical Huffman table has overflowed. The PRETREE case can write beyond the 104-entry PRETREE_table into adjacent heap state in struct LZXstate when reached through chm_open, chm_retrieve_object, LZXdecompress, and BUILD_TABLE. This produces heap memory corruption in the parser process, while arbitrary code execution has not been demonstrated. No fixed version is available as of this review.",
  "id": "CVE-2026-55586",
  "modified": "2026-08-23T03:42:58.201431412Z",
  "published": "2026-08-20T16:35:07.359Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55586.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/sumatrapdfreader/sumatrapdf/security/advisories/GHSA-m423-rp8p-whj8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55586"
    },
    {
      "type": "FIX",
      "url": "https://github.com/sumatrapdfreader/sumatrapdf/commit/13b3d4204dd12d93d426f2157b157b149edc29bf"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "SumatraPDF: Heap out-of-bounds write in vendored CHMLib LZX Huffman table construction reachable from crafted CHM files"
}