In short in Firefox 112, it is possible to check existence of firewalled web servers. This doesn't work in Chrome and Chromium 112 for me.
If user A has tcp connection to web server B, then in the following html: <iframe src="http://B"; onload="load()" onerror="alert('error')" id="i1" /> the javascript function load() will get executed if B serves valid document to A's browser and will not be executed otherwise. This work for both http and https, and for http it is allowed B to be IP address. Under some configurations of Apache2, it serves http despite having https configured. In some sense, this is close to nmap via javascript in a browser. Potential privacy implication is when the attacker guess the range of firewalled IPs and check them all in a loop. For online test: https://j.ludost.net/onload1.html -- guninski: https://j.ludost.net/resumegg.pdf _______________________________________________ Sent through the Full Disclosure mailing list https://nmap.org/mailman/listinfo/fulldisclosure Web Archives & RSS: https://seclists.org/fulldisclosure/
