How Proxies Work: Filtering Traffic, Blocking Malware, and Enabling Attacks

A proxy is a network intermediary that operates at Layer 7 of the OSI model, opening data packets to inspect their contents rather than simply checking source and destination addresses. Forward proxies sit between internal users and the internet, allowing organizations to filter content, block malware, and cache data for faster browsing. In corporate environments, forward proxies can neutralize malware by forcing all outbound traffic through a monitored checkpoint, with Windows-native malware often inadvertently exposing itself by routing through system proxy settings. Reverse proxies, by contrast, monitor inbound traffic and are commonly exploited by attackers to bypass firewalls and evade intrusion detection systems using techniques like SSH tunneling. Proxies can operate either transparently, without the client's knowledge, or non-transparently, depending on how they are configured.