CVE-2026-69148

### Summary The `_validate_source_run` and `_validate_source_model` functions in `mlflow/server/handlers.py` verify that a model version source path is within the artifact directory of a specified run or logged model, but do not check whether the caller has READ permission on that run or model. An authenticated MLflow user can therefore reference another user's run_id in `CreateModelVersion`, creating a model version whose artifact URI points at the victim's artifact directory. If the calling user has MANAGE permission on the registered model (which they do after creation), they can then read arbitrary files from the victim's artifact directory via `GET /model-versions/get-artifact`, bypassing the experiment-level READ permission gate on `GET /get-artifact`. ### Details `POST /api/2.0/mlflow/model-versions/create` is protected: the caller must have UPDATE permission on the registered model. However, the source/run_id validation performed inside `_validate_source_run` only verifies path containment, not caller authorization: ```python # mlflow/server/handlers.py _validate_source_run() def _validate_source_run(source: str, run_id: str) -> None: if is_local_uri(source): if run_id: store = _get_tracking_store() run = store.get_run(run_id) # <-- no permission check on run_id source = pathlib.Path(local_file_uri_to_path(source)).resolve() if is_local_uri(run.info.artifact_uri): run_artifact_dir = pathlib.Path(...).resolve() if run_artifact_dir in [source, *source.parents]: return # validation passes raise MlflowException(...) ``` After creation, the model version's `source` and `run_id` point at the victim's artifact directory. The caller can read files from that directory via the model version artifact handler, which derives the artifact path from the stored `source`: ``` GET /model-versions/get-artifact?name=<model