Handlebars.java provides logic-less and semantic Mustache templates with Java. Prior to 4.5.2, applications that pass user-controlled input to Handlebars.compile() using FileTemplateLoader or ClassPathTemplateLoader are vulnerable to path traversal, allowing arbitrary file read through template names derived from URL path parameters, request parameters, or other user-controlled sources. This issue is fixed in version 4.5.2.
https://github.com/jknack/handlebars.java/security/advisories/GHSA-r4gv-qr8j-p3pg
https://github.com/jknack/handlebars.java/releases/tag/v4.5.2
https://github.com/jknack/handlebars.java/commit/d177cdee8b750385ca7a0d0f89f2d4be73e28f4e