{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0.7.5"
              },
              {
                "last_affected": "0.7.6"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "063c9bb86e14bae7441d2e37ab7207d9839a98ce"
            },
            {
              "last_affected": "512a354dbd31e1895647df852d1565f9d408ed91"
            }
          ],
          "repo": "https://github.com/boazsegev/facil.io",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-125"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66731.json"
  },
  "details": "facil.io 0.7.5 through 0.7.6 contains a denial-of-service vulnerability in the HTTP/1.1 chunked transfer encoding parser that allows unauthenticated remote attackers to crash the server by sending a negative chunk size value. Attackers can send a single POST request with a Transfer-Encoding: chunked header containing a leading minus sign in the chunk size field, causing the parser in http1_parser.h to compute a large positive integer from the negated value, corrupting internal state and moving the read pointer into unmapped memory resulting in a fault.",
  "id": "CVE-2026-66731",
  "modified": "2026-08-12T03:51:47.914507106Z",
  "published": "2026-07-27T16:57:01.077Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/66xxx/CVE-2026-66731.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-66731"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/facil-io-http-chunked-transfer-encoding-parser-crash-dos"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/boazsegev/facil.io"
    },
    {
      "type": "EVIDENCE",
      "url": "https://github.com/theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crash"
    },
    {
      "type": "EVIDENCE",
      "url": "https://tpaidakis.com/writeups/facilio-parser-dos/"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "facil.io 0.7.5 - 0.7.6 HTTP/1.1 Chunked Transfer Encoding Parser Crash DoS"
}