CVE-2026-120306 is a critical vulnerability in Beta9's tenant image build process where shell commands in tenant image definitions are executed with insufficient isolation. The build worker runs these commands with Buildah using chroot isolation, retaining shared PID, network, IPC namespaces, and running as root with CAP_DAC_OVERRIDE. This allows tenant builds to access and potentially modify the worker container's filesystem, including sensitive binaries and Kubernetes service account tokens. The issue is fixed in worker version 0.1.756 by enforcing OCI isolation with private namespaces and restricting tenant ARG propagation.