This indicates an attempt to exploit a Cache Poisoning vulnerability in Squid.
The vulnerability is due to improper checking of Host header against the URI in the HTTP request. By sending a crafted HTTP request to the attacker controlled website, an attacker can poison Squid proxy's cache with arbitrary content.
Squid Project Squid 3.5.12
System compromise: attackers can poison Squid proxy's cache with arbitrary content.
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