Collected research

VPN Extensions are not for privacy

filedescriptor · XSS Jigsaw · 29 October 2018

Browser VPN extensions are really proxy extensions driven by a PAC script, and the usual mistakes in those scripts leak the user's real address. Calling dnsResolve hands every hostname to the ISP, while misused helpers such as shExpMatch, dnsDomainIs and isPlainHostName, substring host whitelists, non-HTTP schemes and Chrome DNS prefetching let any site force a request that skips the proxy.

Record

Researcher

filedescriptor

Published by

XSS Jigsaw

Date

29 October 2018

Topic

Browser

In the archive

• Collected in the 2018 research round

Tags

• browser-extension
• proxy
• dns
• info-leak
• filter-bypass
• url-parsing
• javascript
• survey
• owasp-a05-2021

This page is the archive's own catalogue record. The research is the work of filedescriptor, first published at the original source. Preserved copies are kept so the citation survives its host; this one was last captured on 9 August 2026.