Collected research

Quick Proxy Detection

Quick Proxy Detection ha.ckers.org web application security lab

Firefox accepts bracketed IPv6 notation around an IPv4 literal, so http://[123.123.123.123]/img.jpg loads fine in the browser. Apache's proxy does not understand that syntax and will not fetch it, so an embedded image tag with a unique id reveals whether the visitor is behind a proxy. False positives come from cross-domain blockers and same-domain robots.

Record

Document

Quick Proxy Detection ha.ckers.org web application security lab

Published by

ha.ckers.org

Topic

HTTP

In the archive

• Collected in the 2010 research round

Tags

• proxy
• detection
• url-parsing
• info-leak
• parser-differential
• owasp-a09-2021

This page is the archive's own catalogue record. The research is the work of ha.ckers.org, 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.