We have a Fortigate perimeter firewall, and today I detected this event.

  • What should I do to improve protection?
  • How can someone obtain local IP address through a firewall?

The following alert was observed:

     date=2019-06-18 time=14:35:25 devname=xxxx devid=FG200ETK18901992 
     logid="0419016384" type="utm" subtype="ips" eventtype="signature" 
     level="alert" vd="root" eventtime=1560848725 severity="medium" srcip=y.y.y.y
     srccountry="aaaaaa" dstip=x.x.x.x srcintf="wan1" srcintfrole="wan"
     dstintf="port1" dstintfrole="lan" sessionid=158214294 
action="dropped" proto=6 service="HTTP" policyid=40 attack="WebRTC.Local.IP.Addresses.Disclosure" srcport=80 dstport=57383 

hostname="pxlclnmdecom-a.akamaihd.net" direction="incoming" attackid=40038 
profile="default" ref="http://www.fortinet.com/ids/VID40038" 
incidentserialno=13903968 msg="web_app3: 
WebRTC.Local.IP.Addresses.Disclosure," crscore=10 crlevel="medium"...

It appears the offending traffic was dropped, since your output contains action="dropped".

Searching for your exact title led me to the FortiGuard Encyclopedia, which explains the issue:

This indicates an attempt to obtain the IP addresses of a user through WebRTC in various browsers. The issue is due to a design in various browsers when handling WebRTC calls that probes STUN server to obtain a user's IP address. A potentially malicious actor can exploit this to obtain a user's local and public IP addresses, via a crafted web page.

Further, the same page links to some example JavaScript code that demonstrates how this works.


This was dropped by the Fortigate so there is nothing to change. The issue with this is the disclosure of the internal network. To check/fix your browsers go here: https://browserleaks.com/webrtc#webrtc-disable

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