Vulnerability-Lookup

OSEC-2026-16

Vulnerability from osv_ocaml

Published

2026-08-20 18:15

Modified

2026-08-22 11:05

Summary

Path traversal in Cohttp.Path.resolve_local_file

Details

The issue is that the function normalizes the URI path before percent decoding it:

let resolve_local_file ~docroot ~uri =

  let path = Uri.(pct_decode (path (resolve "http" (of_string "/") uri))) in

  ...

Because %2f is decoded after Uri.resolve, encoded separators survive dot-segment normalization. For example, a request path like:

/static/..%2f..%2f..%2fetc/passwd

is normalized as a single encoded segment, then decoded into:

/static/../../../etc/passwd

afterwards.

Timeline

Aug 11th 2026: report to security@ocaml.org
Aug 14th 2026: PR published on https://github.com/mirage/ocaml-cohttp/pull/1145
Aug 20th 2026: fix released in v6.3.0 https://github.com/ocaml/opam-repository/pull/30528

Severity

8.7 (High)


                    
                      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

Credits

Sapphire Livingstone

Anil Madhavapeddy

Michael Dales

Edwin Torok

Patrick Ferris

Hannes Mehnert

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "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"
        ],
        "opam_constraint": "cohttp {\u003c \"6.3.0\"}"
      },
      "package": {
        "ecosystem": "opam",
        "name": "cohttp",
        "purl": "pkg:opam/cohttp"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5f5a65ec3289c1cd8072bdf0ef22c181b4f11356"
            }
          ],
          "repo": "https://github.com/mirage/ocaml-cohttp.git",
          "type": "GIT"
        }
      ],
      "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"
      ]
    }
  ],
  "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": {
    "cwe": [
      "CWE-22"
    ],
    "human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-16.md",
    "osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-16.json"
  },
  "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 \u003chttps://github.com/mirage/ocaml-cohttp/pull/1145\u003e\n- Aug 20th 2026: fix released in v6.3.0 \u003chttps://github.com/ocaml/opam-repository/pull/30528\u003e",
  "id": "OSEC-2026-16",
  "modified": "2026-08-22T11:05:00Z",
  "published": "2026-08-20T18:15:00Z",
  "references": [],
  "schema_version": "1.7.4",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Path traversal in Cohttp.Path.resolve_local_file"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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