TECHNICAL TEARDOWN: MAYBANK PHISHING MALWARE – PART 1

Posted on February 8, 2016 Updated on February 8, 2016

Recently, Jacob discovered 2 interesting phishing websites,http://maybankk2u%5Bdot%5Dcom  and http://maybank2u-my%5Bdot%5DcomThis 2 websites had the same identical codes and come with a malware in it.

The malware that we discovered is a file infector virus. It scans the system for .html files, .exe and autorun.inf and insert malicious codes into the files.

[ Sample used in the analysis ]
MD5: 44A604F9D96368A83DF55E19644321D3
SHA1: CDBF41310DAE6EFF1127BB92A217369FD2F90B37896568D4F34528AC20468B5C
Malware Sample: index page
Password is “infected29A”

[Backdoor Analysis]
A brief high level overview of the malware infection process flow.

Figure 1 – Infection process

[ Initial Exploitation ]
The backdoor was dropped onto victims’ machine via a malicious VBScript in phishing home page.

Figure 2 – Maybank Phishing homepage

[ VBScript analysis ]
Scrolling down the html source of the webpage, you will come across a large chunk of alphanumeric text. If you look closer at the start of this large chunk of text, you will see the hexadecimal “0x5A4D” which stands for MZ in ascii. Files that start with a MZ header suggests that it is a PE file. You may refer to the following website http://wiki.osdev.org/PE for more information about PE files.

To download the payload you may either run the VBScript (which I don’t really recommend) or simply copy the entire hexadecimal wall of text into a hex editor and save it as a .exe file.

Figure 3 – MZ header spotted

Figure 4 – Dropping malware into temporary folder

When the VBScript is executed, it drops an executable into the targets’ temp folder. The file names are hard-coded as the malware author is probably trying to hide the malware in plain sight by using a common windows executable name, svchost.exe

The details of the extracted malware from the HTML is as follows:
SHA256: FD6C69C345F1E32924F0A5BB7393E191B393A78D58E2C6413B03CED7482F2320
VirusTotal Report: 50/54 (link); 2016-02-03 11:56:14 UTC
Compiled Date/Time: 2008-02-12 11:02:20
Packed: UPX

Let’s unpack the malware using UPX tool itself.

Figure 5 –Unpacking using upx -d

The details of the unpacked malware is as follows:
SHA256:876C5CEA11BBBCBE4089A3D0E8F95244CF855D3668E9BF06A97D8E20C1FF237C
VirusTotal Report: 44/54 (link); 2016-02-02 23:21:33 UTC
Compiled Date/Time: 2008:02:12 12:02:20+01:00

The malware camouflage itself as a bitdefender management console. Another interesting thing to note is that both the product version and the file version seems to be an ip address (106.42.73.61).

Figure 6 – Possibly IP address

[ Dynamic Analysis ]
Let’s begin our journey in analyzing this piece of malware. The malware author had used anti reversing techniques to deter malware analyst from reversing it. Using IDA Pro to see the binary isn’t of much use. Using Procmon surface some interesting stuff.

Figure 7 –New file dropped

As we can see from Figure 7, the malware is writing a new executable into “C:\Program Files\Microsoft\DesktopLayer.exe“. After examining the hashes of the newly dropped executable, I can conclude that the malware simply copy and pasted itself into the new location.

Figure 8 – Executing DesktopLayer.exe

After the file has been copied to the new location, A ProcessCreate function is called to execute the newly dropped executable. The current executable will then terminates.

Figure 9 – Executing Default Browser

Analyzing DesktopLayer.exe via olly debugger shows that the malware is attempting to run the default browser in the operating system. For this case here, it is attempting to execute IEXPLORE.EXE. On further examination, we will notice that the malware is actually trying to write process memory into the suspended IEXPLORE.exe process. This technique is known as process hollowing. Once the malware has finished writing its code into IEXPLORE.EXE process, it will then resume the suspended thread.

Figure 10 – Mutex

Based on Figure 10 taken from process explorer tool. We can observe that the malware uses a unique string (KyUffThOkYwRRtgPP) as it’s mutex.

It is also noted that the malware adds the following key into the registry “HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit“. By doing so, it is able to maintain it persistency in the victims’ machine.

Figure 11 – Persistent Registry Key

To get the actual malware codes that is running off IEXPLORE.exe, we would need to attach ollydbg into the running process and by using the OllyDumpEx plugin we can dump out the running process.

The dumped process contains some interesting strings.

Figure 12 – Script Tags and Autorun?

There are some more interesting strings in the dump that suggests that there is an Antidote for this virus. It also contained the mutex key and a domain name.

Figure 13 – Antidote is available

I am interested in using the antidote. Analyzing the injected process memory dump we come to this assembly codes. To activate the “Antidot”, we would just need to add a registry key; “HKLM\Software\WASAntidot\disable“.

Figure 14 – Disable Malware

As shown in Figure 15, we can prevent mass infection of the virus by adding the registry key as earlier . We even get to see a nice message box telling us that Antidot is activated.

Figure 15 – Antidot Activated

The malware loop through the folders in the victims’ machine and edit all html file it come across with the same malicious code we found in the phishing website. It also attempts to infect suitable .exe files with malicious codes. Once these infected executable gets executed, a copy of the same malware will be dropped and executed on the machine.

The malware also infects removable drives by editing the autorun.inf and planting itself in the RECYCLER sub folder. Better unplug your removable drives from the VM before you try analysing this!

The malware attempts to resolve a domain, fget-career.com. It also attempts to resolve google.com.

Figure 16 – DNS queries in Wireshark

Figure 17 – Spawning Shell

Once the malware calls fget-career url. It can executes shell on the target machine if commands are given.

Figure 18 – Open port 4678

The malware also attempts to listen on port 4678.

Figure 19 – Port 4678 Opened

One of the common ways to find infected or breached systems that most AV companies use is using IOC.  We should be looking for known (or suspicious) command and control (C&C) traffic on the network and looking for known bad or suspicious indicators on the hosts.

Based on our dynamic analysis, below are the known IOC that we can scan our PCs.

[ Host based Indicator ]

1. Mutex – KyUffThOkYwRRtgPP
2. File – C:\Program Files\Microsoft\DesktopLayer.exe
3. File – temp folder\svchost.exe
4. Registry Key – HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit
5. Process – Default Browser with no parent
6. C:\Program Files\Internet Explorer\complete.dat (Default browser path)
7. C:\Program Files\Internet Explorer\dmlconf.dat (Default browser path)

[ Network based Indicator ]

1. fget-career.com (DNS)
2. User Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)
3. Listener on port 4678

[ Whois information ]

Domain Name: MAYBANKK2U.COM
Registrar: CHENGDU WEST DIMENSION DIGITAL TECHNOLOGY CO., LTD.
Sponsoring Registrar IANA ID: 1556
Whois Server: whois.west263.com
Referral URL: http://www.west.cn
Name Server: NS3.MYHOSTADMIN.NET
Name Server: NS4.MYHOSTADMIN.NET
Status: ok https://www.icann.org/epp#OK
Updated Date: 02-feb-2016
Creation Date: 02-feb-2016
Expiration Date: 02-feb-2017

IP Address:  207.226.137.64

Domain Name: MAYBANK2U-MY.COM
Registrar: CHENGDU WEST DIMENSION DIGITAL TECHNOLOGY CO., LTD.
Sponsoring Registrar IANA ID: 1556
Whois Server: whois.west263.com
Referral URL: http://www.west.cn
Name Server: NS3.MYHOSTADMIN.NET
Name Server: NS4.MYHOSTADMIN.NET
Status: ok http://www.icann.org/epp#OK
Updated Date: 02-feb-2016
Creation Date: 02-feb-2016
Expiration Date: 02-feb-2017

IP Address:  207.226.137.64

Once again network whois on the suspicious ip we got from the product version earlier on points back to China.

However, based on the analysis done on the malware and based on passive DNS and past whois records from Virustotal and who.is, the ip address we got from product version earlier could likely to be a fake to throw us off.

Another thing to note is that fget-career.com seems to be offline at the moment and it will be expiring in March 2016. Therefore if we are interested to know/plot the infection widespread of this malware or to takeover this malware we can attempt to buy this domain and host our own C&C server.

Source:http://www.vxsecurity.sg/