[UNDERTOW-2598] CVE-2025-9784 Prevent the dispatch of an exchange if the connection has been closed

Signed-off-by: Flavia Rainone <frainone@redhat.com>

Author: fl4via

core/src/main/java/io/undertow/server/HttpServerExchange.java

@@ -893,6 +893,10 @@ public HttpServerExchange dispatch(final Executor executor, final HttpHandler ha
         final Runnable runnable = new Runnable() {
             @Override
             public void run() {
+                // avoid dispatching when the connection is no longer opened
+                if (!connection.isOpen()) {
+                    return;
+                }
                 Connectors.executeRootHandler(handler, HttpServerExchange.this);
             }
         };