A vulnerability in "nltk.app.wordnet_app" up to version 3.9.3 allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when started in its default mode. The server listens on all interfaces and processes a specific unauthenticated GET request ("/SHUTDOWN%20THE%20SERVER") to terminate the process immediately via "os._exit(0)". This results in a denial of service, impacting service availability. The issue arises due to insufficient authentication and protection mechanisms for critical server functions.