MONAI (Medical Open Network for AI) is an AI toolkit for health care imaging. Prior to 1.6.1, PydicomReader._get_affine() trusts non-finite values in the DICOM PixelSpacing, ImagePositionPatient, and ImageOrientationPatient fields and composes them into an affine matrix without validation. An unauthenticated attacker who can upload a crafted DICOM to a default MONAILabel deployment can propagate NaN or infinity values through LoadImaged, Spacingd, model inference, and output writing, causing inference failures, persistent datastore poisoning, or geometrically corrupted results. This issue is fixed in version 1.6.1.

Affected: PyPI: monai

### Summary

An unauthenticated remote attacker can crash a running MONAILabel server or silently corrupt its medical AI inference results by uploading a single crafted DICOM file (~132 KB) via the REST API. The vulnerability stems from pydicom's lack of validation for Decimal String (DS) and Integer String (IS) DICOM Value Representations, which allows NaN and infinity values to pass through MONAI's PydicomReader and propagate through the entire spatial transform and ML inference pipeline.

No authentication is required for the default MONAILabel REST API. The attacker needs only network access to the server (default port 8000).

**Severity:** CVSS 3.1: 8.7 HIGH **CVSS Vector:** CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:L **CWE:** CWE-20 (Improper Input Validation) → CWE-682 (Incorrect Calculation)

### Details

**Root Cause — Layer 1: pydicom accepts invalid VR values**

pydicom's `DSfloat.__new__()` calls Python's `float(val)`, which silently accepts "NaN", "inf", and "-inf". The DICOM standard (PS3.5 Table 6.2-1) defines DS as digits 0-9, +, -, ., e only. NaN and inf are not valid DS values. The `is_valid_ds()` check only runs in RAISE validation mode, which is NOT the default. The default mode is WARN, which still returns the invalid value.

```python >>> from pydicom.valuerep import DSfloat >>> DSfloat("NaN") nan # Accepted silently — should be rejected >>> DSfloat("inf") inf # Accepted silently — should be rejected ```

This affects ALL pydicom versions fro…