{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 0.22.1"
      },
      "package": {
        "ecosystem": "NuGet",
        "name": "Zio"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.22.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-179",
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-18T00:55:19Z",
    "nvd_published_at": null,
    "severity": "LOW"
  },
  "details": "# Summary\n\n`SubFileSystem` fails to confine operations to its declared sub path when the input path is `/../` (or equivalents `/../`, `/..\\\\`). This path passes all validation but resolves to the root of the parent filesystem, allowing directory level operations outside the intended boundary.\n\n# Affected Component\n\n`Zio.UPath.ValidateAndNormalize`\n`Zio.FileSystems.SubFileSystem`\n\n`UPath.ValidateAndNormalize` has a trailing slash optimisation.\n\n```csharp\nif (!processParts \u0026\u0026 i + 1 == path.Length)\n    return path.Substring(0, path.Length - 1);\n```\n\nWhen the input ends with `/` or `\\`, and `processParts` is still false, the function strips the trailing separator and returns immediately before the `..` resolution logic runs.  The input `/../` triggers this path: the trailing `/` is the last character, `processParts` has not been set (because `..` as the first relative segment after root is specifically exempted), so the function returns `/..` with the `..` segment unresolved.\n\nThe resulting `UPath` with `FullName = \"/..\"` is absolute, contains no control characters, and no colon so it passes `FileSystem.ValidatePath` without rejection.\n\nWhen this path reaches `SubFileSystem.ConvertPathToDelegate`:\n\n```csharp\nprotected override UPath ConvertPathToDelegate(UPath path)\n{\n    var safePath = path.ToRelative();     // \"/..\".ToRelative() = \"..\"\n    return SubPath / safePath;            // \"/jail\" / \"..\" = \"/\"  (resolved by Combine)\n}\n```\n\nThe delegate filesystem receives `/` (the root) instead of a path under `/jail`.\n\n# Proof of Concept\n\n```csharp\nusing Zio;\nusing Zio.FileSystems;\n\nvar root = new MemoryFileSystem();\nroot.CreateDirectory(\"/sandbox\");\nvar sub = new SubFileSystem(root, \"/sandbox\");\n\nConsole.WriteLine(sub.DirectoryExists(\"/../\"));           // True (sees parent root)\nConsole.WriteLine(sub.ConvertPathToInternal(\"/../\"));     // \"/\" (parent root path)\n```\n\n# Impact\n\nThe escape is limited to directory level operations because appending a filename after `..` (e.g., `/../file.txt`) causes normal `..` resolution to trigger, which correctly rejects the path as going above root.  Only the bare terminal `/../` (which strips to `/..`) survives.  This means that exploitability is limited, and this vulnerability does not escalate to file read/write.",
  "id": "GHSA-h39g-6x3c-7fq9",
  "modified": "2026-04-18T00:55:19Z",
  "published": "2026-04-18T00:55:19Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/xoofx/zio/security/advisories/GHSA-h39g-6x3c-7fq9"
    },
    {
      "type": "WEB",
      "url": "https://github.com/xoofx/zio/commit/c8c2f5328e50c1e7ab8c5c405fe70e0bd35f4782"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/xoofx/zio"
    },
    {
      "type": "WEB",
      "url": "https://github.com/xoofx/zio/releases/tag/0.22.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Zio has SubFileSystem Path Confinement Bypass via Unresolved `..` Segment"
}