Threat Level: green Handler on Duty: Johannes Ullrich

SANS ISC: Tool to Detect Active Phishing Attacks Using Unicode Look-Alike Domains - SANS Internet Storm Center SANS ISC InfoSec Forums


Sign Up for Free!   Forgot Password?
Log In or Sign Up for Free!
Tool to Detect Active Phishing Attacks Using Unicode Look-Alike Domains

[This is a guest diary contributed by Remco Verhoef. If you would like to contribute a guest post, please let us know via our contact page]

Currently there is a campaign going on where phishing attacks will use domains that look exactly like safe domains by using Punycode domains. (https://www.wordfence.com/blog/2017/04/chrome-firefox-unicode-phishing/)

This is called a homograph attack. The Punycode domains will start with xn-- prefix and browsers will show the decoded Unicode domain name in the address bar where the Unicode characters  (homographs) used appears like the original characters.

I wrote a program to look for similar characters within a font, comparing exact matches of glyphs. Outputting the table below. It shows the (ASCII) character with the homograph(s). Each font could have different homographs. For Phishing campaigns not only homograph domains could be used, but also the glyphs with small changes. Besides the program to built the table, I’ve created a program that will verify domains to see if they will have a (visually) exact match with a safe domain. Both programs are currently not open source, but will upon request.

 

When using for example URL (courtesy of Xudong Zheng)  https://www.xn--80ak6aa92e.com/, you’ll see (in Firefox and Chrome) in your address bar https://www.apple.com/.

It is possible to request SSL certificates (using e.g., Let’s Encrypt) with Punycode domain names, making this attack even more dangerous. The address bar will appear secure and contain the safe domain name. Impossible to recognize the difference.

We’ve found the following safe domain alternatives. These are probably tip of the iceberg. These domains are exact counterparts of the safe domains. Some companies register a lot of the homograph domains themselves. Google for example, but it seems they forgot a few.

Punycode domain

Unicode domain

Safe domain

Registrar safe domain

Registrar homograph domain

xn--q1a6b.com

ci.com

ci.com

CI Investments Inc.

Privacy Protection

xn--goole-tmc.com

google.com

google.com

Google

Proxy Protection LLC

xn--ooie-z7bc.com

googie.com

google.com

Google

WHOISGUARD PROTECTED

xn--instaram-3sd.com

instagram.com

instagram.com

Instagram, LLC

WHOISGUARD PROTECTED

xn--teleram-cfd.com

telegram.com

telegram.com

Gatehouse Media, LLC

Shield Digital Security Group

xn--hatsapp-h41c.com

whatsapp.com

whatsapp.com

Whatsapp Inc.

Rafael Fernández López (private)

xn--yutube-i15b.com

youtube.com

youtube.com

MARKMONITOR INC.

Anna Potepa (private)

xn--80ak6aa92e.com

apple.com

apple.com

CSC CORPORATE DOMAINS, INC.

Contact Privacy Inc. Customer 1241053230

This is the domain of Xudong Zheng.

xn--q1a6b.com

ci.com

ci.com

CI Investments Inc.

Privacy Protection


Firefox, Chrome, and Opera browsers are vulnerable to the homograph attack, whereas the latest Chrome will contain a fix for this issue. Within Firefox the support for Punycode can be disabled by navigating to about:config and disabling “network.IDN_show_punycode”.

Resources:

https://www.wordfence.com/blog/2017/04/chrome-firefox-unicode-phishing/

https://en.wikipedia.org/wiki/IDN_homograph_attack

https://www.punycoder.com/

https://unicode-table.com/en/

https://www.xudongz.com/blog/2017/idn-phishing/

https://isc.sans.edu/forums/diary/This+Article+is+Brought+to+You+By+the+Letter+12494/20319

 

Johannes

3064 Posts
ISC Handler
Thanks for the write-up!

One small remark though: disabling “network.IDN_show_punycode” in Firefox's about:config may be misunderstood.
Setting "network.IDN_show_punycode" to "true" means that punycode is shown, for example xn--80ak6aa92e.com
Setting "network.IDN_show_punycode" to "false" (default) means that the intended text is shown, for example apple.com
Erik van Straten

122 Posts Posts
Any legitimate business reason to allow punycode domains?
Anonymous

Posts
Any legitimate business reason to allow punycode domains?
Anonymous

Posts
Guess this is a good reason to get EV cert.
Mike7

42 Posts Posts
I did some testing, and it appears to me that Outlook 2016 Version 1702 Build 7870.2038 is vulnerable in the same way as Chrome/Firefox, it shows https://www.epic.com when it should show as https://xn--e1awd7f.com/ if it behaved the same as IE.
Mark

1 Posts Posts
Thx, you're right.
Anonymous

Posts
Yes, these are intended for international use. For example, using the punycoded domain "xn--s7y.co" is equal to the Chinese domain "短.co" which is a legitimate website. Not everyone on the internet uses English, this accommodates for domain addresses in other languages.
Anonymous

Posts
Great post, thank you. Any plans on making the program opensource?
threatsurfer

1 Posts Posts
We developed a tool to check domain names punycode alternatives.

You can use it for your or any domain names.

Github link:
https://github.com/anilyuk/punydomaincheck
Anonymous

Posts

Sign Up for Free or Log In to start participating in the conversation!