medium CVSS 5.6 EPSS <0.1%

CVE-2026-40602·Python vulnerability

The Home Assistant Command-line interface (hass-cli) is a command-line tool for Home Assistant. Up to 1.0.0 of home-assitant-cli an unrestricted environment was used to handle Jninja2 templates instead of a sandboxed one. The user-supplied input within Jinja2 templates was rendered locally with no restrictions. This gave users access to Python's internals and extended the scope of templating beyond the intended usage. This vulnerability is fixed in 1.0.0.

Severity
medium
Software
Python
Fixed in
1.0.0
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 5% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

Until: 1.0.0

Fixed in: 1.0.0

How to fix this CVE

Update the Home Assistant Command-line interface (hass-cli) to version 1.0.0 or later to remediate the Jinja2 template sandbox escape vulnerability. The vulnerable versions allowed unrestricted access to Python internals through template rendering, enabling potential code execution. Ensure your installation uses the patched release and verify the update is correctly applied.

sudo dnf update python3-homeassistant-cli

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'hass-cli --version' or check pip show home-assistant-cli to identify the installed version and confirm if it is prior to 1.0.0
  2. Verify hass-cli is installed by running 'which hass-cli' and check its location in the Python environment
  3. Search Home Assistant logs for Jinja2 template rendering errors or suspicious variable access patterns that may indicate exploitation attempts
  4. After patching, re-run 'hass-cli --version' to confirm the version is 1.0.0 or later and validate that template rendering uses the sandboxed environment

FAQ

What is CVE-2026-40602?

CVE-2026-40602 is a sandbox escape vulnerability in Home Assistant CLI (hass-cli) versions before 1.0.0, where Jinja2 templates were rendered without restrictions, allowing attackers to access Python internals and execute unintended code operations.

Is CVE-2026-40602 being actively exploited?

No, this vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, though the attack vector remains valid for users with local access.

What versions of Python are affected by CVE-2026-40602?

The vulnerability affects Home Assistant CLI (hass-cli) versions up to and including 1.0.0. It is not a Python vulnerability per se, but rather a vulnerability in how hass-cli uses the Jinja2 templating engine within Python.

How do I check if my server is vulnerable to CVE-2026-40602?

Run 'pip show home-assistant-cli' or 'hass-cli --version' to check your installed version. If the version is below 1.0.0, your installation is vulnerable.

Does Defensia detect CVE-2026-40602?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Home Assistant CLI is installed on a monitored server, CVE-2026-40602 will appear in your dashboard with remediation steps.

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References

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