Hancitor (AKA Chanitor) observed using multiple attack approaches

Many threat actors use multiple attack vectors to ensure success. The
individuals using Hancitor malware (also known by the name Chanitor)
are no exception and have taken three approaches to deliver the
malware in order to ultimately steal data from their victims. These
techniques include uncommon API abuse and PowerShell methods.

We recently observed Hancitor attacks against some of our FireEye
Exploit Guard customers. The malicious document used to deliver the
Hancitor executable was observed being distributed as an attachment in
email spam. Once downloaded and executed, it drops an intermediate
payload that further downloads a Pony DLL and Vawtrak executable,
which perform data theft and connect to a command and control (C2) server.

Stage 1: Email Delivery

We observed a number of phishing emails that reference an invoice,
as seen in Figure 1. The attachment in these emails is a weaponized
Microsoft Office document containing a malicious macro that – when
enabled – leads to the download of Hancitor.

Figure 1:  Email with a malicious document attached

Stage 2: Macro and Luring Mechanism

Upon opening the attachment, a typical luring mechanism is employed
instructing the victim to enable macros, as seen in Figure 2. FireEye
has observed the attackers behind this campaign using three different approaches.

Figure 2:  Luring the victim to enable macros

First Approach

Unlike other malicious macros, this one is not using APIs directly
to run the payload. Macros can call APIs directly, but normally are
not supposed to run shellcode. The macro used to deliver Hancitor
calls the native Windows API, “CallWindowProc”, which can be used to
interpret and execute shellcode, as depicted in Figure 3.

Figure 3:  Code within the macro that uses the
CallWindowProc API to execute shellcode

Second Approach

Recently, FireEye Exploit Guard captured Hancitor samples that
leverage a new API Callback function. In addition to “CallWindowProc”,
Hancitor samples may use the function EnumResourceTypesA to interpret
and execute shellcode, as seen in Figure 4.

Figure 4:  EnumResourceTypesA API declaration

Third Approach

We also observed a third approach used by a malicious document file
to deliver Hancitor. Although the threat actor and command and control
servers are similar to the second Hancitor delivery approach, this one
uses an alternate tactic to reach its goal of data theft.

With this approach, the luring message shown in the Figure 2 now
serves another purpose. Not only does it lure the victim into enabling
the macros, but it also is assigned an alternate text: “fkwarning”, as
seen in Figure 5. The macro has code to check this attribute to make
sure the luring message shape object is present. If this object is not
found, the macro will exit without downloading additional payloads.

Figure 5:  Code to ensure that the luring
message is intact and the malicious document is executed for the
first time

Even if it finds the luring message, it will run the macro once and
will delete the shape so that the macro will never be executed again,
as seen in Figure 6.

Figure 6: Code to delete the shape that includes
the lure message

The malicious macro replaces the deleted image with another that
displays the text “network error” to reduce user suspicions, as shown
in Figure 7. Note that text is always present in the malicious macro,
but it will only be made visible by the macro when it is executing for
the first time.

Figure 7: The hidden text that becomes visible
once the macro is executed for the first time

The macro then combines fragments of code to make a PowerShell
command. However, unlike in the other approaches, the malicious code
is not hidden in the code or form or metadata. We observed that the
malware extracts malicious code fragments from within the
section_header of the embedded image and combines them into a
PowerShell command on the fly, as seen in Figure 8. This technique
will evade some basic static methods of detection applied to macros
macro forms.

Figure 8:  PowerShell command observed in header
after increasing font size

The malware authors have taken a very simple but interesting
approach to obscure the PowerShell command text. The font size is set
to microscopic level 1, as seen in Figure 9. This reduces the
likelihood that a casual observer will notice something unusual.

Figure 9:  Minimal font size to hide content of header

Using the “DownloadFile” method, PowerShell obtains a payload from
an attacker-controlled website in a ZIP archive format. PowerShell
uses the “copyhere” function to unzip the payload. The “.Item”
attribute is also set to “16”, which ignores all warnings, as seen in
Figure 10.

Figure 10: Code to download archived payload and
unzip it

Once the downloaded executable is extracted from the ZIP archive,
the macro code deletes the archive using the “Kill” function, as seen
in Figure 11. After the executable is executed, it downloads Pony and
Vawtrak malware variants to steal data.

Figure 11:  Code to delete the archive

Different Approaches, Same Hancitor

Although there are differences between the second and third
approaches to distributing Hancitor, the objective of the threat actor
is the same, as we found the same command and control server being
used in both approaches.

However, we can see a minor change in the second Hancitor approach
command and control servers when compared to the first Hancitor
approach command and control servers, with URLs ending with
ls5/gate.php instead of ls4/gate.php, as seen in Figure 12.

Figure 12: Earlier and newer Hancitor gates

Stage 3: First stage payload

The file copies itself to “%system32%” and creates a registry run
key entry for persistence. Upon execution, it will communicate with an
attacker-controller website to download a variant of the Pony malware,
“pm.dll” along with a standard Vawtrak trojan.

Stage 4: Second stage payload Pony data exfiltration capabilities

We observed a number of data theft capabilities in the second stage
Pony variant, including:

1) Stealing autocomplete Intelliforms data, which may include user
passwords, as seen in Figure 13.

Figure 13: Stealing the content of the
Intelliforms registry key

2) The unique GUID seen in Figure 14 helps to decrypt credentials
from credential store. There is a good amount of documentation on
various forums on how to use this salted value to access credentials.

Figure 14: Credential stealing

3) Accessing Mozilla saved passwords from “signons.txt,” as seen in
Figure 15.

Figure 15: Accessing Mozilla saved passwords

4) Figure 16 shows the malware code related to theft via accessing
Microsoft OMI Email configuration information. We can also see
registry entries related to storing Outlook Profile, which contains
information about where emails and other data is stored being accessed.

Figure 16:  Malware code for Outlook data theft
via registry access


The malware authors responsible for Hancitor have developed several
capabilities within malicious macros that support malware installation
and data theft. These capabilities include leveraging uncommon APIs
and obscuring malicious PowerShell commands, tactics that made
detection more challenging.

FireEye Exploit Guard
provides organizations with the ability to detect malicious shellcode
in the initial phase of the attack lifecycle, regardless of these
evasion techniques.

FireEye recommends that organizations
block macros in Microsoft Office documents that originate from the
Internet by Group Policy. In all cases, users should be cautious about
enabling macros and should practice vigilance about opening email
messages from untrusted sources.

*** This is a Security Bloggers Network syndicated blog from Threat Research Blog authored by Threat Research Blog. Read the original post at: http://www.fireeye.com/blog/threat-research/2016/09/hancitor_aka_chanit.html