Overview#Proxy Auto-Config (PAC) are files that defines how web browsers and other User-agents can automatically choose the appropriate Proxy Server (access method) for fetching a given URL.
Multiple specifications provide a fall-back when a proxy fails to respond. The browser fetches this Proxy Auto-Config file before requesting other URLs. The URL of the Proxy Auto-Config file is either configured manually or determined automatically by the Web Proxy Auto-Discovery Protocol.Web Proxy Auto-Discovery Protocol are subject to malicious PAC Attacks
Proxy Auto-Config are well known for being a part of SSL-TLS Interception schemes.