This indicates an attack attempt to exploit a Privilege Escalation Vulnerability in Joomla.
The vulnerability is due to lack of input validation while handling ACL rulesets. Successful exploitation can lead can cause write ACL violations.
Joomla! 1.7.0 through 3.9.22
Privilege Escalation: Remote attackers can leverage their privileges on vulnerable systems.
Apply the most recent upgrade or patch from the vendor.