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Published on February 13th, 2023 📆 | 3207 Views ⚑

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Phishing Campaign Leverages WOFF Obfuscation and Telegram Channels for Communication

Text to Speech Demo

FireEye Email
Security recently encountered various phishing campaigns, mostly
in the Americas and Europe, using source code obfuscation with
compromised or bad domains. These domains were masquerading as
authentic websites and stole personal information such as credit card
data. The stolen information was then shared to cross-platform,
cloud-based instant messaging applications.

Coming off a busy holiday season with a massive surge in deliveries,
this post highlights a phishing campaign involving a fake DHL tracking
page. While phishing attacks targeting users of shipping services is
not new, the techniques used in these examples are more complex than
what would be found in an off-the-shelf phishing kit.

This campaign uses a WOFF-based substitution cypher, localization
specific targeting, and various evasion techniques which we unravel
here in this blog.

Attack Flow

The attack starts with an email imitating DHL, as seen in Figure
1. The email tries to trick the recipient into clicking on a
link, which would take them to a fake DHL website. In Figure 2, we can
see the fake page asking for credit card details that, if submitted,
would give the user a generic response while in the background the
credit card data is shared with the attackers.

Figure 1: DHL phishing attempt

Figure 2: Fake website imitating DHL tracking

This DHL phishing campaign uses a rare technique for obfuscating its
source page. The page source contains proper strings, valid tags, and
appropriate formatting, but contains encoded text that would render
gibberish without decoding prior to loading the page, as seen in
Figure 3. Typically, decoding such text is done by including script
functions within the code. Yet in this case, the decoding functions
are not contained in the script.

Figure 3: Snippet of the encoded text on
page source

The decoding is done by a Web Open Font Format (WOFF) font file,
which happens upon loading the page in a browser and will not be
visible in the page content itself. Figure 4 shows the substitution
cipher method and the WOFF font file. The attacker does this to evade
detection by security vendors. Many security vendors use static or
regex signature-based rules, so this method will break those
naïve-based conditions.

Figure 4: WOFF substitution cipher

Loading this custom font which decodes the text is done inside the
Cascading Style Sheets (CSS). This technique is rare as JavaScript
functions are traditionally used to encrypt and decrypt HTML text.

Figure 5: CSS file for loading WOFF font file

Figure 5 shows the CSS file used to load the WOFF font file. We have
also seen the same CSS file, style.css, being hosted on the following domains:

• hxxps://www.lifepointecc[.]com/wp-content/sinin/style.css
• hxxps://candyman-shop[.]com/auth/DHL_HOME/style.css
• hxxps://mail.rsi-insure[.]com/vendor/ship/dhexpress/style.css
• hxxps://www.scriptarticle[.]com/thro/HOME/style.css

These legitimate-looking domains are not hosting any phishing
websites as of now; instead, they appear to be a repository for
attackers to use in their phishing campaigns. We have seen similar
phishing attacks targeting the banking sector in the past, but this is
newer for delivery websites.  

Notable Techniques

Localization

The phishing page displays the local language based on the region of
the targeted user. The localization code (Figure 6) supports major
languages spoken in Europe and the Americas such as Spanish, English,
and Portuguese.

Figure 6: Localization code

The backend contains PHP resource files for each supported language
(Figure 7), which are picked up dynamically based on the user’s IP
address location.

Figure 7: Language resource files

Evasion

This campaign employs a variety of techniques to evade detection.
This will not serve up a phishing page if the request came from
certain blocked IP addresses. The backend code (Figure 8) served the
users with a "HTTP/1.1 403 Forbidden" response header under
the following conditions:

• IP has been seen five times (AntiBomb_User func)
• IP
  host resolves to its list of avoided host names ('google',
  'Altavista', 'Israel', 'M247', 'barracuda', 'niw.com.au' and more)
  (AntiBomb_WordBoot func)
• IP is on its own local blocklist
  csv (x.csv in the kit) (AntiBomb_Boot func)
• IP has seen
  POSTing three times (AntiBomb_Block func)

Figure 8: Backend evasion code

After looking at the list of blocked hosts, we could deduce that the
attackers were trying to block web crawlers.

Data Theft

The attackers behind this phishing campaign attempted to steal
credentials, credit card data, and other sensitive information. The
stolen data is sent to email addresses and Telegram channels
controlled by the attacker. We uncovered a Telegram channel where data
is being sent using the Telegram Bot API shown in Figure 9.

Figure 9: Chat log

While using php mail() function to send stolen credentials is
quite common, in the near past, encrypted instant messaging
applications such as Telegram have been used for sending phished
information back to command and control servers.

We were able to access one of the Telegram channels controlled by
the attacker as shown in Figure 10. The sensitive information being
sent in the chat includes IP addresses and credit card data.

Figure 10: Telegram channel with stolen information

Conclusion

Attackers (and especially phishers) are always on the hunt for new
ways to evade detection by security products. Obfuscation gives the
attackers an edge, and makes it harder for security vendors to protect
their customers.

By using instant messaging applications, attackers get user data in
real time and victims have little to respond once their personal
information is compromised.

Indicators of Compromise (IOC)

FireEye Email Security utilizing FAUDE (FireEye Advanced URL
Detection Engine) protects customers from these types of phishing
threats. Unlike traditional anti-phishing techniques dependent on
static inspection of phishing URL content, FAUDE uses multiple
artificial intelligence (AI) and machine learning (ML) engines to more
effectively thwart these attacks.

From December 2020 until the time of posting, our FAUDE detection
engine saw more than 100 unique URLs hosting DHL phishing pages with
obfuscated source code, including:

• hxxps://bit[.]ly/2KJ03RH
• hxxps://greencannabisstore[.]com/0258/redirect-new.php
• hxxps://directcallsolutions[.]co[.]za/CONTACT/DHL_HOME/
• hxxps://danapluss[.]com/wp-admin/dhl/home/
• hxxp://r.cloudcyberlink[.]digital/ (multiple paths
  using same domain)

Email Addresses

• medmox2k@yandex[.]com
• o.spammer@yandex[.]com
• cameleonanas2@gmail[.]com

Telegram Users

• @Saitama330
• @cameleon9

style.css

• Md5: 83b9653d14c8f7fb95d6ed6a4a3f18eb)
• Sha256:
  D79ec35dc8277aff48adaf9df3ddd5b3e18ac7013e8c374510624ae37cdfba31

font-woff2

• MD5: b051d61b693c76f7a6a5f639177fb820
• SHA-256:
  5dd216ad75ced5dd6acfb48d1ae11ba66fb373c26da7fc5efbdad9fd1c14f6e3

Domains

URLs

Source link

Tagged with: campaign • channels • communication • leverages • obfuscation • phishing • telegram • WOFF