GHSA-wx9m-wx4f-4cmg: 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 doesA 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):On Linux only, the function:Returns early if `MISTRAL_INIT` is already set in the environment.Sets `MISTRAL_INIT=1` so the spawned child does not re-trigger the dropper if it imports `mistralai`.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.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 `import mistralai`, not package installation. `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 and were not analyzed in this advisory. The behavior of the second-stage payload on the host is therefore unknown.RecommendationAny 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 (per the timing reported in #523).Check whether you are affectedInstalled version:Dependency files and lockfiles:Dropped file on disk: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.RemediationPin `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`.On affected Linux hosts, rotate every credential reachable from the importing process and review host and cloud audit logs.Indicators of compromiseAll IOCs below come from the public report in [#523](https://github.com/mistralai/client-python/issues/523).File: `/tmp/transformers.pyz`Process: a Python interpreter (`sys.executable`) running `/tmp/transformers.pyz` detached from the parent's process group, with stdout/stderr to `/dev/null`Environment variable: `MISTRAL_INIT=1`Outbound HTTPS to `83[.]142[.]209[.]194` from `curl` (no TLS verification)Function added to the package: `_run_background_task` in `src/mistralai/client/__init__.py`SHA-256 of the malicious sdist (as reported in #523): `6dbaa43bf2f3c0d3cddbca74967e952da563fb974c1ef9d4ecbb2e58e41fe81b`ReferencesPublic report with the dropper code: https://github.com/mistralai/client-python/issues/523Quarantined PyPI project: https://pypi.org/project/mistralai/
CVSS v3.1: 9.6