A (Still in Development) monitoring browser extension for pages acting as bad boys.
NB: This is the code repository of the project, if you're looking for the packed extensions:
Firefox: https://addons.mozilla.org/en-US/firefox/addon/behave/
Chrome: https://chrome.google.com/webstore/detail/mppjbkhgconmemoeagfbgilblohhcica/

Introduction.
Behave! monitors and warn if a web page performs any of following actions:

• Browser based Port Scan
• Access to Private IPs
• DNS Rebinding attacks to Private IPs

Here's Behave! pointing the finger to at.tack.er page in the logs:


Port Scan Monitoring
Behave! will alert the user if the number of port or protocol used during a browser session exceeds a specific limit.
The limit is 20 by default, but it can be changed by the user via preferences.
Since Behave does not perform any DNS request,

Direct access to Private IPs Monitoring
Behave! will alert if a web page tries to directly access to an IP belonging to any the following blocks:

• Loopback addresses IPv4 127.0.0.1/8
• Loopback addresses IPv6 ::1/128
• Private Networks IPv4 10.0.0.0/8 - 172.16.0.0/12 - 192.168.0.0/16
• Unique Local Addresses IPv6 fc00::/7

DNS Resolution to Private IPs
If a malicious script instructs the Browser to connect to a FQDN whose authoritative DNS resolves to a private IP Behave! checks if the resolved IP is private. Anyway, the IP information of a resolved hostname is available only if the port is open.
Since Behave!, in order to prevent TOCTOU issues, does not perform any external DNS request, if the port is closed there will be no IP resolution available and therefore, no alert.

DNS Rebinding Bypasses
Behave! does not perform any direct DNS request, and the IP is taken from the intercepted response.
That means that it's not exposed to any TOCTOU attack like DNS Rebinding.

DNS Rebinding Monitoring
Behave! keeps track if a hostname is resolved with multiple IPs, and will alert if there's some mixing between public IPs and private ones.

Install
Behave! is available as packed extension on:
Firefox Extension: https://addons.mozilla.org/en-US/firefox/addon/behave/
Chrome Extension: https://chrome.google.com/webstore/detail/mppjbkhgconmemoeagfbgilblohhcica/
However, if like you want to play a bit with the code you can:

• Clone it OR download the zip and unzip
• Open Google Chrome/Chromium go to chrome://extension
• Activate Developer Mode
• Push "Load Unpacked" and choose the Behave directory.
• Enjoy Behave!

Wanna Test Behave! ?
See what happens when you go to one of the following:
Singularity of Origin DNS Rebinding Attack: http://rebind.it:8080/manager.html
JavaScript Port Scan: http://jsscan.sourceforge.net/jsscan2.html
Nota Bene: At the moment it won't alert if DNS Rebinding attack is performed on non private IPs such as: http://www.alf.nu/BrowserCacheAndDnsRebinding

Wanna Help?
You are welcome to help! Feel free to create an Issue or fork the project and make a PR.