Proxy Auto-Config (PAC) files in Firefox < 51 can specify a JavaScript function called for all URL requests with the full URL path which exposes more information than would be sent to the proxy itself in the case of HTTPS. Normally the Proxy Auto-Config file is specified by the user or machine owner and presumed to be non-malicious, but if a user has enabled Web Proxy Auto Detect (WPAD) this file can be served remotely.
Proxy Auto-Config (PAC) files in Firefox < 51 can specify a JavaScript function called for all URL requests with the full URL path which exposes more information than would be sent to the proxy itself in the case of HTTPS. Normally the Proxy Auto-Config file is specified by the user or machine owner and presumed to be non-malicious, but if a user has enabled Web Proxy Auto Detect (WPAD) this file can be served remotely.
https://www.mozilla.org/en-US/security/advisories/mfsa2017-01/#CVE-2017-5384 https://bugzilla.mozilla.org/show_bug.cgi?id=1255474
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