CVE-2026-63490: Handlebars.java: Arbitrary file read in `SpringTemplateLoader` via URL-fragment suffix bypass

com.github.jknack.handlebars.springmvc.SpringTemplateLoader resolves Spring MVC view names into URLs via Spring’s ResourceLoader without applying the path-containment check that protects every other URL-based loader in the project (ClassPathTemplateLoader, FileTemplateLoader, ServletContextTemplateLoader - all hardened by commit d177cdee).

The only remaining defense for file: / classpath: view names is the unconditional .hbs suffix appended by AbstractTemplateLoader.resolve(...). This suffix is the load-bearing security boundary that prevents a request like view=file:/etc/passwd from reading /etc/passwd instead of /etc/passwd.hbs.

This boundary is bypassed by a single character: # (the URL fragment delimiter).

When the view name ends with #, the appended .hbs lands inside the URL fragment. Both Spring’s FileUrlResource.exists() (via URI.getSchemeSpecificPart()) and the JDK’s URL.openStream() (via URL.getFile()) silently discard the fragment, so the file actually opened is the bare path the attacker specified - for example /etc/passwd rather than /etc/passwd.hbs. The compiled “template” is then parsed and rendered into the HTTP response body.

Result: unauthenticated, network-reachable, arbitrary file read of any file readable by the JVM process on any Spring MVC application that uses a default-configured HandlebarsViewResolver and exposes a controller that returns a (fully or partly) user-influenced view name.