CVE-2026-27905

BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Prior to 1.4.36, the safe_extract_tarfile() function validates that each tar member's path is within the destination directory, but for symlink members it only validates the symlink's own path, not the symlink's target. An attacker can create a malicious bento/model tar file containing a symlink pointing outside the extraction directory, followed by a regular file that writes through the symlink, achieving arbitrary file write on the host filesystem. This vulnerability is fixed in 1.4.36.

An adversary publishes a malicious model to a public registry (e.g., HuggingFace Hub) targeting BentoML users. The bento archive contains: (1) a symlink 'models/config' pointing to '/etc/cron.d', and (2) a regular file 'models/config/pwned' containing a reverse shell cronjob. BentoML's safe_extract_tarfile() validates the symlink's own path as safe but fails to validate the symlink target. During extraction, step 1 creates the symlink pointing outside the extraction root; step 2 writes through it, depositing the reverse shell at /etc/cron.d/pwned. The cron daemon executes the payload within minutes, establishing persistent access to the model server. In CI/CD environments, this could compromise build agents and inject malicious code into downstream model artifacts before they reach production.