A critical Remote Code Execution (RCE) vulnerability was identified in the server-side template rendering mechanism used by the Glassfish gadget handler. The application processes .xml files and evaluates user-supplied values within a context where Expression Language (EL) “expressions” are processed without proper sanitization or escaping. By injecting expressions such as #{7*7}, the server returns 49, confirming server-side EL evaluation. This issue allows a remote attacker to fully compromise the underlying host, enabling capabilities as reading/modifying data, executing arbitrary commands, persistence, and lateral movement. This issue affects Eclipse GlassFish: from 8.0.0 to 8.0.1, fixed in 8.0.2; 7.1.0, fixed in 7.1.1; from 7.0.0 to 7.0.25, fixed in 7.0.26. Impact on versions from 5.1.0 to 6.2.5 is unknown.