{
  "schema_version": "1.7.4",
  "id": "OSEC-2026-16",
  "modified": "2026-08-22T11:05:00Z",
  "published": "2026-08-20T18:15:00Z",
  "summary": "Path traversal in Cohttp.Path.resolve_local_file",
  "details": "The issue is that the function normalizes the URI path before percent\ndecoding it:\n\n```OCaml\nlet resolve_local_file ~docroot ~uri =\n\n  let path = Uri.(pct_decode (path (resolve \"http\" (of_string \"/\") uri))) in\n\n  ...\n```\n\nBecause `%2f` is decoded after Uri.resolve, encoded separators survive\ndot-segment normalization. For example, a request path like:\n\n```\n/static/..%2f..%2f..%2fetc/passwd\n```\n\nis normalized as a single encoded segment, then decoded into:\n\n```\n/static/../../../etc/passwd\n```\n\nafterwards.\n\n## Timeline\n\n- Aug 11th 2026: report to security@ocaml.org\n- Aug 14th 2026: PR published on <https://github.com/mirage/ocaml-cohttp/pull/1145>\n- Aug 20th 2026: fix released in v6.3.0 <https://github.com/ocaml/opam-repository/pull/30528>",
  "severity": [
    {
      "type": "CVSS_V4",
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/S:N/AU:Y/R:A/V:D/RE:M"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "opam",
        "name": "cohttp",
        "purl": "pkg:opam/cohttp"
      },
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.3.0"
            }
          ]
        },
        {
          "type": "GIT",
          "repo": "https://github.com/mirage/ocaml-cohttp.git",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5f5a65ec3289c1cd8072bdf0ef22c181b4f11356"
            }
          ]
        }
      ],
      "versions": [
        "0.9.1",
        "0.9.2",
        "0.9.3",
        "0.9.4",
        "0.9.5",
        "0.9.6",
        "0.9.7",
        "0.9.8",
        "0.9.9",
        "0.9.10",
        "0.9.11",
        "0.9.12",
        "0.9.13",
        "0.9.14",
        "0.9.15",
        "0.9.16",
        "0.10.0",
        "0.10.1",
        "0.11.0",
        "0.11.1",
        "0.11.2",
        "0.12.0",
        "0.13.0",
        "0.14.0",
        "0.15.0",
        "0.15.1",
        "0.15.2",
        "0.16.0",
        "0.16.1",
        "0.17.0",
        "0.17.1",
        "0.17.2",
        "0.18.0",
        "0.18.1",
        "0.18.2",
        "0.18.3",
        "0.19.0",
        "0.19.1",
        "0.19.2",
        "0.19.3",
        "0.20.0",
        "0.20.1",
        "0.20.2",
        "0.21.0",
        "0.21.1",
        "0.22.0",
        "0.99.0",
        "1.0.0",
        "1.0.2",
        "1.1.0",
        "1.1.1",
        "1.2.0",
        "2.0.0",
        "2.1.2",
        "2.1.3",
        "2.2.0",
        "2.3.0",
        "2.4.0",
        "2.5.0",
        "2.5.1",
        "2.5.2",
        "2.5.2-1",
        "2.5.3",
        "2.5.4",
        "2.5.5",
        "2.5.6",
        "2.5.7",
        "2.5.8",
        "3.0.0",
        "4.0.0",
        "4.1.1",
        "4.1.2",
        "5.0.0",
        "5.1.0",
        "5.2.0",
        "5.3.0",
        "5.3.1",
        "6.0.0~alpha0",
        "6.0.0~alpha1",
        "6.0.0~alpha2",
        "6.0.0~beta2",
        "6.0.0",
        "6.1.0",
        "6.1.1",
        "6.2.1",
        "6.2.2"
      ],
      "ecosystem_specific": {
        "opam_constraint": "cohttp {< \"6.3.0\"}",
        "affected_bindings": [
          "Cohttp.Path.resolve_local_file",
          "Cohttp_async.Server.resolve_local_file",
          "Cohttp_lwt_unix.Server.resolve_file",
          "Cohttp_lwt.Make().resolve_local_file"
        ]
      }
    }
  ],
  "references": [],
  "credits": [
    {
      "name": "Sapphire Livingstone",
      "type": "REPORTER"
    },
    {
      "name": "Sapphire Livingstone",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Anil Madhavapeddy",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Anil Madhavapeddy",
      "type": "REMEDIATION_REVIEWER"
    },
    {
      "name": "Michael Dales",
      "type": "REMEDIATION_REVIEWER"
    },
    {
      "name": "Edwin Torok",
      "type": "REMEDIATION_REVIEWER"
    },
    {
      "name": "Patrick Ferris",
      "type": "REMEDIATION_REVIEWER"
    },
    {
      "name": "Hannes Mehnert",
      "type": "COORDINATOR"
    }
  ],
  "database_specific": {
    "osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-16.json",
    "human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-16.md",
    "cwe": [
      "CWE-22"
    ]
  }
}