Of Phishing Attacks and WordPress 0days

by Marc Rogers.

Proxying around 5% of the Internet’s requests gives us an interesting vantage point from which to observe malicious behavior. However, it also makes us a target. Aside from the many and varied denial of service (DDoS) attacks that break against our defenses, we also see huge number of phishing campaigns. In this blog post I'll dissect a recent phishing attack that we detected and neutralized with the help of our friends at Bluehost.

One attack that is particularly interesting because it appears to be using a brand new WordPress 0day.

A Day Out Phishing

The first sign we typically see that indicate a new phishing campaign is underway are the phishing emails themselves. Generally, there's a constant background noise from a few of these emails targeting individual customers every day. However, when a larger campaign starts up that trickle typically turns into a flood of similar messages.

Here's an example we've recently received:
Example Phish Note — CloudFlare will never send you an email like this. If you see one like it, it is fake and should be reported to our abuse team by forwarding it to support@cloudflare.com.

In terms of the phishing campaign timeline, these emails aren’t the first event. Much like a spider looking to trap flies, a phisher first has to build a web to trap his or her victims. One way is through landing pages.

Looking like the legitimate login page of a target domain, these landing pages have one goal - to collect your credentials. Since these landing pages are quickly identified, the phisher will often go to great lengths to ensure that he or she can put up tens or even hundreds of pages during the lifetime of a campaign, all while being extra careful that these pages can't be traced back to him or her. Generally, this means compromising a large number of vulnerable websites in order to inject a phishing toolkit.

It's no surprise that first step in most phishing campaigns will usually be the mass compromise of a large number of vulnerable websites. This is why you will often see a notable uptick in the volume of phishing emails whenever a major vulnerability comes out for one of the popular CMS platforms. This is also why protecting the Internet’s back-office is a critical step in building a better Internet. If vulnerable CMS sites are protected, not only can they flourish, but the thousands of potential victims that could get abused when their infrastructure gets hijacked for malicious purposes are also protected.

This is why, at CloudFlare, we feel that providing free, basic security to every website is such important thing and why ultimately it could be such a game changer in building a better Internet.

Back to the phish

Returning to our phishing attack, we see that it's no different. Analyzing the “load.cloudflare.com” hyperlink on the message, we see that it's actually a link pointing to a compromised WordPress site hosted by Bluehost.

Note: This is not a reflection on Bluehost, every hosting provider gets targeted at some point. What's more important is how those hosting providers subsequently respond to reports of compromised sites. In fact, Bluehost should be commended for the speed with which they responded to our requests and the way they handled the affected sites we reported.

Every other email in this particular campaign followed the same pattern. Here is the source for another one of those links that uses “activate.cloudflare.com”:

As you can see, while the message will display that you are going to “activate.cloudflare.com”, in reality, anyone that clicks on the link will be diverted to the victim website. Which, unsurprisingly, is running an old, vulnerable version of WordPress.

Every phishing email from this campaign has followed exactly the same pattern: a basic email template addressed to $customer informing them that their site has been locked, and inviting them to click on a link that takes them to a compromised WordPress site on Bluehost.

It looks like is this attacker harvested a large number of target domains using public DNS and email records identifying administrative email addresses. This became the victim list. The attacker then targeted a convenient, vulnerable CMS platform and injected his or her phishing kit into every innocent domain that's been compromised. Finally, once that is complete the attacker will send out the phishing emails to the victim list.

As phishing attacks go, this one is remarkably unsophisticated. All a savvy user had to do to reveal the true nature of this link is a quick mouse over. As soon as you do mouse over, the link you will see -- “activate.cloudflare.com” -- does not match the true destination.

More advanced phishing techniques

A clever phisher could have used one of the many well known tricks to obfuscate the URL. Below are some of those techniques possible so you will know them if you see them.

  • Image Maps. Instead of using a traditional hyperlink as above, phishers have been known to put an image map in their emails. The image, of course, is of a link to a trusted site such as “www.safesite.com”. When an unsuspecting user clicks within the coordinates of the image map, they are diverted to the phishing site.

Here's an example of this technique taken from an old eBay phishing email:

In order to fool Bayesian filters looking for phishing spam like this, the phisher also added some legitimate sounding words in white font to keep them from appearing. The user experience, however, is the same as the earlier phishing email. As soon as you mouse over the image map, you will see the true destination.

  • Misspelled domain names and homoglyphs. Misspelled domains can look very similar to their legitimate counterparts and by using a homoglyph -- or look-a-like character -- an attacker can make a misspelling look even less obvious. Examples include “microsft.com” or “g00gle.com” These domains look so similar to the advertised link in the phishing email that many people will miss the discrepancy when they mouse over the link.

  • Reflection, Redirection, and javascript. Many websites -- even sites like answers.usa.gov -- have search features, offsite links, or vulnerable pages that have historically been abused by phishers. If the offsite link can be manipulated, typically with a cross site scripting vulnerability, it's possible for the phisher to present a link from the target domain that takes the victim to a page under the Phisher’s control. Below is an example of a historic flaw of this nature that existed on the answers.usa.gov site

    In this case, the URL looks like a legitimate “answers.usa.gov” ur,l but if you clicked on it, you would activate a cross-site scripting flaw that executes the javascript in your browser. The attacker could easily turn a page with this sort of flaw into a malicious credential harvester, all while continuing to use a link to the legitimate site.

    Note - All those extra %20’s are encoded spaces to push the javascript far enough away that it won’t be visible on mouse over.

    A slightly different flaw, also on the USA.gov site, involved its URL shortening service. Open to anyone, Phishers quickly discovered that they could use this service to create shortened URLs that looked important because of the .gov prefix. A victim that might be reluctant to click on an unsolicited bit.ly link might be less reluctant if faced with a .gov link. Here's an example of an email from a campaign abusing that service:

  • URL obfuscation. Historically, this has been one of the most popular and varied techniques. The concept is simple: use any of the available URL encoding methods to disguise the true nature of the destination URL. I'll describe a couple of historic techniques below.

    Note: many modern browsers now warn against some of these techniques.

    First is username:password@url abuse. This notation, now deprecated because only an idiot would pass credentials in the HTTP query string these days, was designed to allow seamless access to password protected areas. Abuse is easy, for example:

    www.safesite.com@www.evilsite.com

    Next is IP address obfuscation. You are probably familiar with the IP address as a dotted quad? 123.123.123.123 Well, IP addresses can also be expressed in a number of other formats which browsers will accept. By combining this with the “username:password@” trick above, an attacker can effectively hide his true destination. Below are four different methods for presenting one of Google’s IP addresses -- 74.125.131.105

    All of these URLs go to 74.125.131.150.

    Finally we have Punycode and Homoglyph based obfuscation. Punycode was created as a way for international characters to map to valid characters for DNS, e.g., “café.com”. Using punycode this would be represented as xn--caf-dma.com. As mentioned at the start, homoglyphs are symbols which closely resemble other symbols, like 0 and O, or I and l.

    By combining these two methods we can create URLs like:

    www.safesite.com⁄login.html.evilsite.com

    The secret to this obfuscated URL is to use a non-standard character which happens to be a homoglyph for /. The result? Instead of a page on safesite.com, you are actually taken to a subdomain of the following punycode domain:

    www.safesite.xn--comlogin-g03d.html.evilsite.com

    New obfuscation techniques like these appear all the time. Phishing is both the most common and arguably the most effective method of attack for medium to low skill attackers. Staying up to date with these techniques can be extremely useful when it comes to spotting potential phishing attempts.

Conclusions

After further analysis, it quickly became clear that all of the endpoints in this campaign were compromised WordPress sites running WordPress 4.0 - 4.1.1.

The most likely scenario is that a new critical vulnerability has surfaced in WordPress 4.1.1 and earlier. Given that 4.1.1 was, at the time of writing, the most current version of WordPress, this can only mean one thing -- a WordPress 0day in the wild.

Checking the WordPress site confirms that that a few hours ago they announced a new critical cross-site scripting vulnerability:

WordPress Security Notice

While we can’t confirm for certain that this is the vulnerability our phisher was using, it seems highly likely given the version numbers compromised.

Over the last few hours, we've worked closely with our friends at Bluehost to identify the remaining affected sites compromised by this phisher so they could take them offline. A quick response like this essentially renders all remaining phishing emails in this current campaign harmless. The need to quickly neutralize Phishing sites is why CloudFlare engineers developed our own process for rapidly identifying and tagging suspected compromised sites. When a site on our network is flagged as phishing site, we impose an interstitial page that serves to both to warn potential visitors and give the site owner time to fix the issue.

You can read more about our own process in this blog post.

How customers can stay safe

By enabling the CloudFlare's WAF, CloudFlare customers have some protection against the sort of cross-site scripting vulnerability involved in this attack. However, anyone can still fall victim to a phishing email. Below are 7 tips to help you stay safe:

  • NEVER click on links in unsolicited emails or advertisements.
  • Be vigilant, poor spelling and strange URLs are dead giveaways.
  • Mouse over the URL and see if it matches the what’s presented in the email.
  • Type URLs in manually where possible.
  • Stay up to date on your software and make sure you are running a current up-to-date antivirus client — yes, even if you're using Mac.
  • It’s possible to set traps for phishers: use unique, specific email addresses for each account you set up. That way if you get an email to you Bank of America email address asking for your Capital One password, you immediately know it's a phishing attack.
  • Finally, where possible enable two-factor authentication. While not foolproof, it makes it much harder for attackers.
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