MLFlow Creates a Temporary File With Insecure Permissions

In mlflow/mlflow versions prior to 3.11.0, the `get_or_create_nfs_tmp_dir()` function in `mlflow/utils/file_utils.py` creates temporary directories with world-writable permissions (0o777), and the `_create_model_downloading_tmp_dir()` function in `mlflow/pyfunc/__init__.py` creates directories with group-writable permissions (0o770). These insecure permissions allow local attackers to tamper with model artifacts, such as cloudpickle-serialized Python objects, and achieve arbitrary code execution when the tampered artifacts are deserialized via `cloudpickle.load()`. This vulnerability is particularly critical in environments with shared NFS mounts, such as Databricks, where NFS is enabled by default. The issue is a continuation of the vulnerability class addressed in CVE-2025-10279, which was only partially fixed.

CVSS 3.0

CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-378

Also known as

BIT-mlflow-2026-4137, CVE-2026-4137, PYSEC-2026-2655

• nvd.nist.gov/vuln/detail/CVE-2026-4137
• github.com/mlflow/mlflow/commit/1dcbb0c2fbd1f446c328830e601ca13a28219b8a
• github.com/mlflow/mlflow/commit/bd8854fb2b4b168a4384ebddc6c4a0b5d56aff01
• github.com/advisories/GHSA-4x5p-f36r-mxxr
• github.com/mlflow/mlflow
• github.com/pypa/advisory-database/tree/main/vulns/mlflow/PYSEC-2026-2655.yaml
• huntr.com/bounties/648dc30b-76c7-4433-86b8-f43d926fd8d6