This indicates an attack attempt to exploit an Information Disclosure vulnerability in Nginx.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a crafted HTTP request. A remote attacker can exploit this to gain unauthorized access to sensitive information.
nginx 0.5.6 - 1.13.2.
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.