A maliciously crafted DICOMDIR ReferencedFileID can point to files outside the intended File‑set root. The library resolves the path only to confirm existence, but does not check that the resolved path remains inside the root. When common FileSet operations such as copy(), write(), or remove()+write(use_existing=True) later use that unchecked path, an attacker can read, copy, and in some flows move or delete arbitrary files. The weakness corresponds to CWE‑22 (Path Traversal). The CVSS score of 7.8 indicates a high severity impact on confidentiality, integrity, and availability.

The vulnerability affects the Python package pydicom, versions 2.0.0‑rc.1 through 3.0.1 inclusive. The issue was fixed in release 3.0.2, so any system using the older versions of this library is potentially exposed. Users of pydicom in any Python environment that processes DICOMDIR files should verify the version they are running.

The attack requires delivery of a crafted DICOMDIR file to an application that imports pydicom and performs FileSet operations such as copy or write. Because the EPSS score is below 1% and the vulnerability is not listed in the CISA KEV catalog, active exploitation is currently low, but the high CVSS score means significant damage is possible if exploited. Industries processing medical imaging data that import DICOMDIR files with pydicom should consider the risk of arbitrary file access if the library is not updated.