osec-2026-08

{
  "affected": [
    {
      "database_specific": {
        "source": "https://github.com/ocaml/security-advisories/blob/generated-osv/2026/OSEC-2026-08.json"
      },
      "ecosystem_specific": {
        "opam_constraint": "tar {< \"3.5.0\"}"
      },
      "package": {
        "ecosystem": "opam",
        "name": "tar",
        "purl": "pkg:opam/tar"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.5.0"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "51ceb0a15982993503c169b9d84456fd50eabe99"
            }
          ],
          "repo": "https://github.com/mirage/ocaml-tar",
          "type": "GIT"
        }
      ],
      "versions": [
        "0.8.0",
        "0.9.0",
        "1.0.0",
        "1.0.1",
        "1.1.0",
        "2.0.0",
        "2.0.1",
        "2.1.0",
        "2.2.0",
        "2.2.1",
        "2.2.2",
        "2.3.0",
        "2.4.0",
        "2.5.0",
        "2.5.1",
        "2.6.0",
        "3.0.0",
        "3.1.1",
        "3.1.2",
        "3.2.0",
        "3.3.0",
        "v3.4.0",
        "v3.3.0",
        "v3.1.1",
        "V3.1.0",
        "v2.4.0",
        "v2.3.0",
        "v2.2.2",
        "v2.2.1",
        "v2.2.0",
        "v2.0.0",
        "v1.1.0",
        "v1.0.1",
        "v1.0.0",
        "v0.9.0",
        "v0.8.0",
        "v0.7.1",
        "v0.7.0",
        "v0.6.1",
        "v0.6.0",
        "v0.5.1",
        "v0.5.0",
        "v0.4.2",
        "v0.4.1",
        "v0.4.0",
        "0.3.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-45390"
  ],
  "credits": [
    {
      "name": "Quentin Stiévenart",
      "type": "REPORTER"
    },
    {
      "name": "Reynir Björnsson",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Anil Madhavapeddy",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Hannes Mehnert",
      "type": "COORDINATOR"
    }
  ],
  "database_specific": {
    "cwe": [
      "CWE-22",
      "CWE-61"
    ],
    "human_link": "https://github.com/ocaml/security-advisories/tree/main/advisories/2026/OSEC-2026-08.md",
    "osv": "https://github.com/ocaml/security-advisories/tree/generated-osv/2026/OSEC-2026-08.json"
  },
  "details": "A malicious archive with `../` path segments in its name allows escaping the current working directory. This is not desired behavior, and tar(1) rejects such extractions, but ocaml-tar decompresses it anyway.\nThe impact is that it allows arbitrary file write outside of the desired extraction directory to an attacker that can reach a tar decompression endpoint. In terms of severity, similar vulnerabilities in different ecosystems (python, node, go) have been assigned CVSS scores of 6.8 MEDIUM, 7.1 HIGH, and 8.2 HIGH.\n\n## Details\n\nFunction `Tar_unix.extract` uses `Filename.concat`.\n\n```OCaml\nlet extract ?(filter = fun _ -> true) ~src dst =\n  let f ?global:_ hdr () =\n    if filter hdr then\n      match hdr.Tar.Header.link_indicator with\n      | Tar.Header.Link.Normal ->\n        begin match Result.map_error unix_err_to_msg\n            (safe Unix.(openfile (Filename.concat dst hdr.Tar.Header.file_name)\n                          [ O_WRONLY ; O_CREAT ]) hdr.Tar.Header.file_mode) with\n        | Error _ as err -> Tar.return err\n        | Ok dst ->\n          try copy ~dst_fd:dst (Int64.to_int hdr.Tar.Header.file_size)\n          with exn -> safe_close dst; Tar.return (Error (`Exn exn))\n        end\n        (* TODO set owner / mode / mtime etc. *)\n      | _ ->\n        (* TODO handle directories, links, etc. *)\n        let open Tar.Syntax in\n        let* () = Tar.seek (Int64.to_int hdr.Tar.Header.file_size) in\n        Tar.return (Ok ())\n    else\n      let open Tar.Syntax in\n      let* () = Tar.seek (Int64.to_int hdr.Tar.Header.file_size) in\n      Tar.return (Ok ())\n  in\n  fold f src ()\n```\n\n`Filename.concat` does not perform any sanitation:\n\n```\n# Filename.concat \"/tmp\" \"../../../etc/passwd\";;\n- : string = \"/tmp/../../../etc/passwd\"\n```\n\nHence, calling `Unix.openfile` on such a path will result in opening `/etc/passwd`.\n\nI only confirmed it in the following setting (see PoC below), and a proper fix would require investigating it in more details:\n\nversion targeted: 3.3.0, which seems to be the only version of ocaml-tar. But use of `Filename.concat` seems to have been there since the beginning.\n\n## Impact\n\nThis is a path traversal vulnerability that allows an attacker to perform an arbitrary file write outside of the intended extraction directory.\nVulnerable users are the users relying on ocaml-tar, which includes (according to the readme of ocaml-tar):\n\n- xapi (confirmed not vulnerable by maintainers)\n- obuilder\n\nRelated CVEs\n\n- CVE-2007-4559: same problem in python's implementation of tar\n- CVE-2025-0377: similar problem in hashicorp's go implementation of tar\n- CVE-2026-24842: similar problem in node-tar\n\n## Fix\n\nThe fix is to sanitize paths before calling `Unix.openfile`. In the presence of symlink support, extra validation is needed.\n\n## Timeline\n\n- 2026-05-07: reported via GitHub (on https://github.com/ocaml/security-advisories)\n- 2025-05-20: initial fix developed and asked for review, also informed xapi and obuilder teams\n- 2025-05-22: fixed tar released, security advisory announced",
  "id": "OSEC-2026-08",
  "modified": "2026-05-22T21:15:04.511594668Z",
  "published": "2026-05-22T20:55:00Z",
  "schema_version": "1.7.5",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Path traversal vulnerability in ocaml-tar"
}