This indicates an attack attempt to exploit an Information Disclosure vulnerability in Joomla content management system.
The vulnerability is due to insufficient validation of user supplied inputs. It allows remote attackers to extract authentication credentials of the LDAP server that is used by the Joomla! installation, such as the username and password of the super user, the Joomla administrator.
Joomla versions before 3.8.0, configured to use LDAP authentication
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.