Arcane: Unauthenticated reflected XSS via SVG color parameter in /api/app-images/logo enables admin account takeover

Arcane is an interface for managing Docker containers, images, networks, and volumes. Prior to 1.19.0, the unauthenticated GET /api/app-images/logo endpoint reflects a user-supplied color query parameter into the body of an SVG document via strings.ReplaceAll with no escaping. The substitution lands inside a <style> element of the embedded logo.svg, allowing an attacker to close the style block and inject executable <script> content. Because the response is served as image/svg+xml and Arcane sets no Content-Security-Policy or X-Content-Type-Options headers, navigating a logged-in admin victim to a crafted URL executes attacker-controlled JavaScript in Arcane's origin and rides the victim's HttpOnly JWT cookie to fully compromise the admin account. This vulnerability is fixed in 1.19.0.