This indicates an attack attempt to exploit a Denial of Service vulnerability in Squid Proxy Cache Manager.
The vulnerability is due to insufficient sanitizing of user supplied inputs in cachemgr.cgi of the application when handling crafted HTTP POST request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
Squid Project Squid 184.108.40.206
Squid Project Squid 3.2 through 3.2.3
Squid Project Squid 3.1 through 3.1.21
Squid Project Squid 3.0
Squid Project Squid 2.x
Server Compromise: Remote Attackers can crash vulnerable systems via denial of service
Currently we are unaware of any vendor working supplied patch for this issue