PAC

A file that tells browsers which proxy to use for given URLs.

Proxy Auto Configuration is a script, typically named with a .pac extension, that tells a browser which proxy to use for a given URL or to connect directly. It centralizes proxy logic so traffic can be routed for filtering, caching, or inspection. Because the browser executes the file, an attacker who can tamper with the PAC file or its delivery, for example through insecure auto-discovery, may redirect a victim's traffic to a malicious proxy. Securing how the file is distributed is therefore important.