AIKIDO-2026-707978

TL;DR

The framework validates the configured themeRoot in validateThemeRoot before creating the theme CSS <link> element that loads style variables. Protocol-relative URLs such as //attacker.example start with /, so they are treated as relative paths and resolved against the current page, producing the attacker origin and bypassing the origin allowlist that is enforced for other absolute cross-origin URLs. An application that lets untrusted input reach the themeRoot configuration therefore loads theme stylesheets from an attacker-controlled origin, enabling external CSS injection. The fix resolves protocol-relative and relative inputs to the current origin and only creates the link element from a validated, normalized theme root.