That example is typical "confused deputy" security vuln irrespective of the language, not a "validate input" one. Meaning, the typical unix interface to the filesystem is such that it's hard/impossible to express "i'm only having access to this folder and interested in paths within that folder". `chroot` is too dramatic sandboxing that cannot be used for all use cases.

BTW, in macOS there are "secure bookmarks" (see NSURL docs) that are effectively capability tokens: when user drags a file, or selects it in an Open File dialog (which runs isolated from the app), the kernel creates an app-specific token that grants access to that file to the app, so it can access it beyond its sandbox.