An MCP host-allowlist regex missing an end anchor lets any lookalike domain through.

GHSA-83x6-42hr-jc76 at CVSS 5.3 covers the CKAN MCP Server, where two tools restrict server_url to dati.gov.it with a regex anchored only at the start and no boundary after the host. Any URL whose host merely begins with dati.gov.it, such as dati.gov.it.attacker.com, or that uses it as userinfo before an @, passes validation while targeting attacker infrastructure. Small bug, but host-allowlist regexes are the default way MCP server authors constrain outbound tool arguments, and this is the exact shape that keeps failing. Parse the URL and compare the host, don't regex the string.