This indicates an attack attempt to exploit a Denial of Service Vulnerability in Squid Project Squid.
The vulnerabilities are due to invalid processing of HTTP Range requests. A remote attacker could exploit these vulnerabilities by sending a crafted request to the target server. Successful exploitation could result in a denial-of-service condition.
Squid Project Squid 4.x prior to 4.15
Squid Project Squid 5.x prior to 5.0.6
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor.