The template upload API endpoint accepted requests from different domain when sent in conjunction with ARP spoofing + man in the middle (MiTM) attack, resulting in a CSRF attack. The required attack vector is complex, requiring a scenario with client certificate authentication, same subnet access, and injecting malicious code into an unprotected (plaintext HTTP) website which the targeted user later visits, but the possible damage warranted a Severe severity level. Mitigation: The fix to apply Cross-Origin Resource Sharing (CORS) policy request filtering was applied on the Apache NiFi 1.8.0 release. Users running a prior 1.x release should upgrade to the appropriate release.