CVE-2026-40602

Workarounds

Evaluate the Jninja2 templates manually or tool-based before rendering with hass-cli.

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.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2026-40602 has a CVSS score of 5.6 (Medium). The vector is requires local access, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.0); upgrading removes the vulnerable code path.

Kodem intelligence

1.0.0 uses ImmutableSandboxedEnvironment and restricts the usage of environment variables.

1. What is CVE-2026-40602? CVE-2026-40602 is a medium-severity code injection vulnerability in homeassistant-cli (pip), affecting versions < 1.0.0. It is fixed in 1.0.0. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2026-40602? CVE-2026-40602 has a CVSS score of 5.6 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of homeassistant-cli are affected by CVE-2026-40602? homeassistant-cli (pip) versions < 1.0.0 is affected.
4. Is there a fix for CVE-2026-40602? Yes. CVE-2026-40602 is fixed in 1.0.0. Upgrade to this version or later.
5. Is CVE-2026-40602 exploitable, and should I be worried? Whether CVE-2026-40602 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-40602 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-40602? Upgrade homeassistant-cli to 1.0.0 or later.