This indicates an attempt to exploit a Denial of Service vulnerability in Squid.
The vulnerability is due to input validation when the vulnerable software handles a malformed TLS request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system, via crafted TLS packets.
Squid Project Squid Prior to 3.5.9
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.