Author: Anton Wendel

Emotet drops ZeuS Panda targeting German and Austrian online banking users

Emotet is currently one of the prevalent threats on the Internet. The former banking trojan is now known to steal passwords and to drop other malware like Dridex on its infected machines. We recently found Emotet spreading Zeus Panda, which presented us with an opportunity to link some of our research on Emotet with our analysis of ZeuS Panda.  The Zeus Panda sample used in this wave is rolled out through Emotet in german-speaking countries and targets online banking users in Germany and Austria.

The Emotet C2 server drops additional malware to infected system. Whether a system receives such a package seems to be based on the geographical location of the infected system in question. After the additional malware is downloaded from the C2 server, it is written to a file in %ALLUSERSPROFILE% (C:\ProgramData in recent Windows versions) with a random name of 4 to 19 characters length and the file extension “.exe”. Emotet is capable of executing this binary in two different ways, either of which is chosen by the C2 server. The first mode executes the malware in the same context that Emotet is running in, the second mode executes the malware in the context of the currently logged-on user.

As stated above, the current wave downloads and executes the well-known ZeuS Panda banking trojan. To know which banking sites it should attack and how to modify the site’s content, the trojan needs so-called webinjects. From the URL masks of the webinjects this sample uses, we can tell that it currently targets online banking customers in Germany and Austria. All injects write a single script reference into the targeted websites. When the targeted site is loaded, the browser loads the referenced script, which is then executed in the context of the banking website. The only difference between the webinjects is the last number in the URL of the script source. This number seems to define the targeted website, which allows the server to deliver a target-specific script. The script actually downloaded is obfuscated by a simple string encryption. The actual script is part of an Automated Transfer System (ATS) which tries to persuade the user into transferring money to an account the attacker specifies.

scriptSchutzanalageRetoureThe above screenshots show an exemplary representation on the modification of the banking websites. They show two different attack scenarios: The first script tries to trick the user into performing an transaction in the guise of a security check. The attackers “inform” the customer of newly installed security measures on the banking website, coercing the user to complete a training using a demo account, before they are able to access their account again. During this training, a real transaction is made in the background to an account that the attacker specifies. The phrasing in the text is lousy and should raise suspicion with most customers.

 

The second script tries to persuade the user that an erroneous transfer was made to their account. It suggests to go to a bank branch or make the return transfer online. Additionally, the script blocks access to the banking account until the return transfer has been completed. The phrasing in the text is better than in the first script and may not raise suspicion at first glance.

The first script resembles word by word the webinject Kaspersky identified during their analysis of Emotet in 2015. At this time Emotet contained its own banking trojan capability and delivered the webinjects directly into the browser. As ZeuS Panda uses the same webinject format as the old Emotet, we can speculate about the reasons:

  • The webinject is acquired from the same creator
  • The group behind Emotet has dropped developing their own banking trojan and acquires such trojans from other malware authors
  • The group behind Emotet developed multiple banking trojans for its own use and for sale

It seems Emotet is not only used to sell distribution of malware, but also used by its owners. It is also possible that the group behind Emotet uses the slim downloader as an entry point for targeted attacks. In this case the group can spread Emotet worldwide and distribute specific malware to each target. As the real malicious payload is only downloaded after some time and only to specific targets, analysts can not directly draw conclusions on the real intention of an infection.

IOCs

Emotet:

C2:

5.9.195.154
45.73.17.164
60.32.214.242
85.25.33.71
194.88.246.242
213.192.1.170
217.13.106.16
217.13.106.246
217.13.106.249

SHA256:

0d25cde8d49e1bcf6a967c0df6ac76992ff129ea5c30a1492a5bedd313e6fb51
c287a9aa25ed6afc54bc5ebe4b098675f3fa4b7cb51fbdcfb50591b4b8fa3b90

ZeuS Panda:

C2:

uamanshe.gdn
ugjeptpyour.top

SHA256:

4fe20a9cf5e5c28ec55aa529179f7fe6df3cda8ae43340b04b2402f43dfefd5f
fbd9e31cc5cbfce2b8135234fdcfdac7fa48a127aa6f3644d05c6ba77bd6d903

Emotet harvests Microsoft Outlook

The original German blog post can be found on the G DATA Blog.

Emotet has been known as a trojan for years. Former versions focused on attacking online banking users, however the current Emotet was  transformed into a downloader and information stealer. The first reports of this new variant were published by CERT Polska in April 2017. Since then, Emotet has been spreading through spam phishing mails containing a link to a Microsoft Word document that acts as dropper for the Emotet binary.

Recently, CERT-Bund again warned about the spam mails which spread Emotet. The sender address of these emails is spoofed to appear as a sender known to the recipient. This strengthens the trust in the mail and increases the probability that the recipient opens the attachment or link without further consideration.

For this to work, the entities spreading Emotet need to have at least superficial knowledge of the social network a target interacts with via email. Acting opportunistically Emotet delivers a specific module to infected systems to harvest all emails in Microsoft Outlook accounts of the current user, allowing it to extract the relations between sender and receiver.

 

MAPI-Functions

To obtain the information from Outlook, the module takes advantage of the standardized interface MAPI. The picture above shows the loading of the MAPI-DLL and the retrieval of the needed functions. Utilizing this interface, the module iterates through all Outlook profiles it can access on the computer. It extracts all E-Mail-Account Names and E-Mail-Addresses from each profile. Afterwards it searches for emails recursively in each folder in the profile. From each mail found it extracts the sender (displayed name and mail address) and all recipients (displayed names and mail addresses) inclusive the recipients in the CC- and BCC-fields and saves them in relation to each other. The picture below shows the extracted fields from the emails. In case a field only contains a reference to an address book entry, the module extracts the name and email address from the address book. In this process only the mail header is evaluated, the content of the mails is not analyzed.

Fields

After the Emotet module has searched all profiles, folders, and emails, it writes the data it has retrieved in a temporary file in the directory %PROGRAMDATA%. The email addresses are sorted descending by how often they occur. Each address is extended with all contacts, that are in relation to it. However, two cases are distinguished:

  • if the referenced contact is the sender of the mail, it is extended with all recipients
  • if the referenced contact is the recipient of the mail, it is only extended with the sender

Example (Mailbox of A):mail

Mail 1: A sends to B and C

Mail 2: D sends to A

Mail 3: C sends to A , D, and E

A is referenced three times and therefore is placed on top of the list. A has a relation to B and C through mail 1, thus B and C get connected with A. Mail 2 shows a connection from D to A, thus D gets connected with A too. The relation from C to A in mail 3 is ignored, because it is already captured in mail 1 (A→C). Mail 3 contains the additional relations C→D and C→E. As no relations between C↔D and C↔E are already in the list, the contacts D and E get assigned to the contact C and are appended to the list.

The complete list, which gets transferred to the attacker, looks like this:

A<A@mail.com>; B<B@mail.com>; C<C@mail.net>; D<D@mail.com>
C<C@mail.net>; D<D@mail.com>; E<E@mail.com>

Afterwards the module encrypts the file, transfers it to the attacker and removes it from disk.

This  allows the attacker to get a condensed but comprehensive overview of the social network graph behind a victims email communications. With such a list, an attacker has knowledge of the relation between persons and can send spam mails with suitable sender header without great afford. Additionally, an attacker learns relations between contacts whose computers are not yet infected.

To deliver the spam mails to the suitable recipients, the attacker needs valid E-Mail accounts. For this task, they use an additional module that is able to extract the credentials from mail programs and transfer them to the attackers. To extract the credentials from all common mail programs, such as Microsoft Outlook, Mozilla Thunderbird, and Windows Mail, this module utilizes an integrated copy of the application Mail PassView from the company NirSoft. It writes this information to a temporary file, which is then encrypted and transfered to the attacker. Once transfered the temporary file is deleted.