Squid is open-source caching proxy software for web traffic. It sits between clients and origin servers, forwarding HTTP requests, reusing cached responses, and enforcing policy controls such as access rules, filtering, and authentication.
In cyber security, Squid matters because a proxy is part of the trust boundary. If it misparses an HTTP request or handles caching incorrectly, attackers may bypass controls, poison cache entries, or cause users to receive altered content. Defenders use Squid to improve performance and visibility, but they also rely on timely patching, strict configuration, and careful handling of unusual HTTP behavior to protect cache integrity and traffic security.