BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Prior to 1.4.39, src/bentoml/ internal/container/frontend/dockerfile/templates/base v2.j2 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. This vulnerability is fixed in 1.4.39.