CVE-2026-40602 is a medium-severity (CVSS 5.6) Code Injection vulnerability in homeassistant-cli. A fix is available for homeassistant-cli — see the affected versions and patch details below.
hass-cli: Handling of user-supplied Jinja2 templates
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40602.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
homeassistant-cliReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Up to 1.0.0 of home-assitant-cli (or hass-cli for short) 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.
E. g., it was possible to render a template with hass-cli template bad-template.j2 --local that contained entries like
{%- set b = environ.__globals__['__builtins__'] -%}
{%- set os = b['__import__']('os') -%}
{%- set bio = b['__import__']('builtins') -%}
...
or other malicious Jinja2 expressions. This can lead to arbitrary code execution on the local machine.
In a two step process an adversary could trick/convince an user to download third-party templates which contain harmful code (e. g., perform data manipulation or establish a remote shell) then to render those templates unchecked/reviewed/verified with --local.
The issue only affect the local machine and not a remote Home Assistant instance. It also requires user interventions.
Patches
1.0.0 uses ImmutableSandboxedEnvironment and restricts the usage of environment variables.
Workarounds
Evaluate the Jninja2 templates manually or tool-based before rendering with hass-cli.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | homeassistant-cli | all versions | 1.0.0pip install --upgrade 'homeassistant-cli==1.0.0' |
Affected Products
home assistant command-line interfacehome-assistant-ecosystemDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for homeassistant-cli, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update homeassistant-cli to 1.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40602 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Frequently Asked Questions
Is CVE-2026-40602 in your dependencies?
Find it across PyPI, including transitive dependencies.