Vault and Vault Enterprise versions prior to 1.16.3 and between 1.17.0 and 1.17.2 improperly handle requests from unauthorized IP addresses when the TCP listener option proxy_protocol_behavior is set to deny_unauthorized. This causes the Vault API server to shut down and stop responding to HTTP requests, resulting in a denial of service. The issue is fixed in versions 1.15.12, 1.16.6, and 1.17.2.