CVE-2026-55878: symfony/ux-toolkit: Path Traversal Allows Arbitrary File Write and Read via Crafted Recipe Manifest

The ux:install console command installs files from a recipe kit by copying paths listed in a copy-files map. The only guard against malicious paths was Path::isRelative(), which returns true for paths like ../../../etc. Path::join() then resolves the .. segments without complaint, so the final path can escape the intended directory entirely. A crafted or compromised kit can therefore write attacker-controlled content to arbitrary locations on the developer’s machine or CI runner.

Because the copy operation creates missing parent directories and can overwrite existing files silently (with --force or in non-interactive environments), an attacker who controls a kit can overwrite files such as controllers, git hooks, or .env to achieve code execution. The source side of copy-files is symmetrically affected, enabling local file reads outside the recipe directory.