CVE-2026-120307 is a critical vulnerability in the Beta9 worker where the sandbox file API is improperly served from outside the container. This flaw allows a tenant with a workspace token and a running sandbox to access and manipulate files on the hosting worker as root, including files belonging to other tenants. The vulnerability arises from path resolution issues that allow directory traversal and symbolic link exploitation, enabling unauthorized file operations on the worker host. The issue is fixed in worker version 0.1.756 by restricting file operations to stay within the container root or mount source.