CVE-2026-71259: ESPHome external_components file:// Scheme Validation Bypass Leading to Remote Code Execution

ESPHome through 2026.7.0-dev contains an operator-precedence bug in the cv.url() validator in esphome/configvalidation.py: if parsed.scheme and parsed.netloc or parsed.scheme == "file": return parsed.geturl(). Because and binds tighter than or, any file: URI passes validation regardless of netloc. This validator gates the url: field of the externalcomponents YAML directive's git source schema, which is passed to git clone (git supports file:// natively). A crafted externalcomponents block with url: "file:///attacker/repo" clones an attacker-controlled local path, which is then added to Python's import machinery via ESPHome's component loader, executing arbitrary Python code when the YAML configuration is processed (e.g. via esphome config/esphome run).