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Cyber Security Tip ST05-016
Understanding Internationalized Domain Names
You may have been exposed to internationalized domain names (IDNs)
without realizing it. While they typically do not affect your browsing
activity, IDNs may give attackers an opportunity to redirect you to a
malicious web page.
What are internationalized domain names?
To decrease the amount of confusion surrounding different languages,
there is a standard for domain names within web browsers. Domain names
are included in the URL (or web address) of web site. This standard is
based on the Roman alphabet (which is used by the English language),
and computers convert the various letters into numerical equivalents.
This code is known as ASCII (American Standard Code for Information
Interchange). However, other languages include characters that do not
translate into this code, which is why internationalized domain names
were introduced.
To compensate for languages that incorporate special characters (such
as Spanish, French or German) or rely completely on character
representation (such as Asian or Arabic languages), a new system had
to be developed. In this new system, the base URL (which is usually
the address for the home page) is dissected and converted into a
format that is compatible with ASCII. The resulting URL (which
contains the string "xn--" as well as a combination of letters and
numbers) will appear in your browser's status bar. In newer versions
of many browsers, it will also appear in the address bar.
What are some security concerns?
Attackers may be able to take advantage of internationalized domain
names to initiate phishing attacks (see Avoiding Social Engineering
and Phishing Attacks for more information). Because there are certain
characters that may appear to be the same but have different ASCII
codes (for example, the Cyrillic "a" and the Latin "a"), an attacker
may be able to "spoof" a web page URL. Instead of going to a
legitimate site, you may be directed to a malicious site, which could
look identical to the real one. If you submit personal or financial
information while on the malicious site, the attacker could collect
that information and then use and/or sell it.
How can you protect yourself?
* Type a URL instead of following a link - Typing a URL into a
browser rather than clicking a link within a web page or email
message will minimize your risk. By doing this, you are more
likely to visit the legitimate site rather than a malicious site
that substitutes similar-looking characters.
* Keep your browser up to date - Older versions of browsers made it
easier for attackers to spoof URLs, but most newer browsers
incorporate certain protections. Instead of displaying the URL
that you "think" you are visiting, most browsers now display the
converted URL with the "xn--" string. Internet Explorer does not
currently support IDNs, so you will see an error message if you
try to visit a URL that includes non-ASCII characters.
* Check your browser's status bar - If you move your mouse over a
link on a web page, the status bar of your browser will usually
display the URL that the link references. If you see a URL that
has an unexpected domain name (such as one with the "xn--" string
mentioned above), you have likely encountered an internationalized
domain name. If you were not expecting an internationalized domain
name or know that the legitimate site should not need one, you may
want to reconsider visiting the site. Browsers such as Mozilla and
Firefox include an option in their security settings about whether
to allow the status bar text to be modified. To prevent attackers
from taking advantage of JavaScript to make it appear that you are
on a legitimate site, you may want to make sure this option is not
enabled.
_________________________________________________________________
Authors: Mindi McDowell, Will Dormann, Jason McCormick
_________________________________________________________________
Produced 2005 by US-CERT, a government organization.
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