This indicates an attack attempt to exploit an Information Disclosure vulnerability in Cisco Firepower Management Center.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted HTTP request. A remote attacker may be able to exploit this to gain unauthorized access to sensitive information, via a crafted HTTP request.
Cisco Firepower Management Center version 6.0.1 and prior
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Upgrade to the latest version available from the vendor.