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Clandestine Fox, Part Deux

We reported at the end of April and the beginning of May on an APT threat group leveraging a zero-day vulnerability in Internet Explorer via phishing email attacks. While Microsoft quickly released a patch to help close the door on future compromises, we have now observed the threat actors behind “Operation Clandestine Fox” shifting their point of attack and using a new vector to target their victims: social networking.

An employee of a company in the energy sector recently received an email with a RAR archive email attachment from a candidate. The attachment, ostensibly containing a resume and sample software program the applicant had written, was from someone we’ll call “Emily” who had previously contacted the actual employee via a popular social network.

FireEye acquired a copy of the suspicious email – shown below in Figure 1 – and attachment from the targeted employee and investigated. The targeted employee confirmed that “Emily” had contacted him via the popular social network, and that, after three weeks of back and forth messaging “she” sent her “resume” to his personal email address.  

clandestine2

Figure 1: Sample email illustrating how “Emily” attacks a victim employee

Working our way backwards, we reviewed “Emily’s” social network profile and noticed a few strange aspects that raised some red flags. For example, “her” list of contacts had a number of people from the victim’s same employer, as well as employees from other energy companies; “she” also did not seem to have many other “friends” that fit “her” alleged persona. “Her” education history also contained some fake entries.

Further research and discussions with the targeted company revealed that “Emily,” posing as a prospective employee, had also contacted other personnel at the same company. She had asked a variety of probing questions, including inquiring who the IT Manager was and what versions of software they ran – all information that would be very useful for an attacker looking to craft an attack.

It’s worth emphasizing that in the instances above, the attackers used a combination of direct contact via social networks as well as contact via email, to communicate with their intended targets and send malicious attachments. In addition, in almost all cases, the attackers used the target’s personal email address, rather than his or her work address. This could be by design, with a view toward circumventing the more comprehensive email security technologies that most companies have deployed, or also due to many people having their social network accounts linked to their personal rather than work email addresses.

Details – Email Attachment #1

The resume.rar archive contained three files: a weaponized version of the open-source TTCalc application (a mathematical big number calculator), a benign text copy of the TTCalc readme file, and a benign PDF of Emily’s resume. The resume was a nearly identical copy of a sample resume available elsewhere on the Internet.  The file details are below.

Filename MD5 Hash
resume.rar 8b42a80b2df48245e45f99c1bdc2ce51
readme.txt 8c6dba68a014f5437c36583bbce0b7a4
resume.pdf ee2328b76c54dc356d864c8e9d05c954
ttcalc.exe e6459971f63612c43321ffb4849339a2

Upon execution, ttcalc.exe drops the two files listed below, and also launches a legitimate copy of TTCalc v0.8.6 as a decoy:

%USERPROFILE%/Application Data/mt.dat
%USERPROFILE%/Start Menu/Programs/Startup/vc.bat

The file mt.dat is the actual malware executable, which we detect as Backdoor.APT.CookieCutter. (Variants of this family of backdoor are also referred to as “Pirpi” in the security industry). In this case, the malware was configured to use the following remote servers for command and control:

    • swe[.]karasoyemlak[.]com
    • inform[.]bedircati[.]com (Note: This domain was also used during Operation Clandestine Fox)
    • 122.49.215.108

 

Metadata for mt.dat:

Description MD5 hash
md5 1a4b710621ef2e69b1f7790ae9b7a288
.text 917c92e8662faf96fffb8ffe7b7c80fb
.rdata 975b458cb80395fa32c9dda759cb3f7b
.data 3ed34de8609cd274e49bbd795f21acc4
.rsrc b1a55ec420dd6d24ff9e762c7b753868
.reloc afd753a42036000ad476dcd81b56b754
Import Hash fad20abf8aa4eda0802504d806280dd7
Compile date 2014-05-27 15:48:13

Contents of vc.bat:

 

@echo offcmd.exe /C start rundll32.exe “C:\Documents and Settings\admin\Application Data\mt.dat” UpdvaMt

Details – Email Attachment #2

Through additional research, we were able to obtain another RAR archive email attachment sent by the same attackers to an employee of another company. Note that while there are a lot of similarities, such as the fake resume and inclusion of TTCalc, there is one major difference, which is the delivery of a completely different malware backdoor. The attachment name this time was “my resume and projects.rar,” but this time it was protected with the password “TTcalc.”

Filename MD5 hash
my resume and projects.rar ab621059de2d1c92c3e7514e4b51751a
SETUP.exe 510b77a4b075f09202209f989582dbea
my resume.pdf d1b1abfcc2d547e1ea1a4bb82294b9a3

SETUP.exe is a self-extracting RAR, which opens the WinRAR window when executed, prompting the user for the location to extract the files. It writes them to a TTCalc folder and tries to launch ttcalcBAK.exe (the malware dropper), but the path is incorrect so it fails with an error message. All of the other files are benign and related to the legitimate TTCalc application.

Filename MD5 hash
CHANGELOG 4692337bf7584f6bda464b9a76d268c1
COPYRIGHT 7cae5757f3ba9fef0a22ca0d56188439
README 1a7ba923c6aa39cc9cb289a17599fce0
ttcalc.chm f86db1905b3f4447eb5728859f9057b5
ttcalc.exe 37c6d1d3054e554e13d40ea42458ebed
ttcalcBAK.exe 3e7430a09a44c0d1000f76c3adc6f4fa

The file ttcalcBAK.exe is also a self-extracting Rar which drops and launches chrome_frame_helper, which is a Backdoor.APT.Kaba (aka PlugX/Sogu) backdoor using a legitimate Chrome executable to load the malicious DLL via side-loading. Although this backdoor is used by multiple threat groups and is quite commonly seen these days, this is the first time we’ve observed this particular threat group using this family of malware. The malware was configured to communicate to the command and control domain www[.]walterclean[.]com (72.52.83.195 at the time of discovery) using the binary TCP protocol only. The file details are below, followed by the malware configuration.

Filename MD5 hash
chrome_frame_helper.dll 98eb249e4ddc4897b8be6fe838051af7
chrome_frame_helper.dll.hlp 1b57a7fad852b1d686c72e96f7837b44
chrome_frame_helper.exe ffb84b8561e49a8db60e0001f630831f

 

Metadata MD5 hash
chrome_frame_helper.dll 98eb249e4ddc4897b8be6fe838051af7
.text dfb4025352a80c2d81b84b37ef00bcd0
.rdata 4457e89f4aec692d8507378694e0a3ba
.data 48de562acb62b469480b8e29821f33b8
.reloc 7a7eed9f2d1807f55a9308e21d81cccd
Import hash 6817b29e9832d8fd85dcbe4af176efb6
Compile date 2014-03-22 11:08:34

 

Backdoor.APT.Kaba Malware Configuration:

PlugX Config (0x150c bytes):

Flags: False True False False False False True True True True False

Timer 1: 60 secs

Timer 2: 60 secs

C&C Address: www[.]walterclean[.]com:443 (TCP)

Install Dir: %ALLUSERSPROFILE%\chrome_frame_helper

Service Name: chrome_frame_helper

Service Disp: chrome_frame_helper

Service Desc: Windows chrome_frame_helper Services

Online Pass: 1234

Memo: 1234

Open Source Intel

The domain walterclean[.]com shares registration details with securitywap[.]com:

The following domains are registered to QQ360LEE@126.COM

Domain: walterclean[.]com
Create Date: 2014-03-26 00:00:00
Registrar: ENOM, INC.

Domain: securitywap[.]com
Create Date: 2014-03-26 00:00:00
Registrar: ENOM, INC.

Conclusion

In short, we attributed these attacks to the same threat actor responsible for “Operation Clandestine Fox,” based on the following linkages:

  • The first-stage malware (mt.dat) is a slightly updated version of the Backdoor.APT.CookieCutter malware dropped during Operation Clandestine Fox
  • Based on our intel, Backdoor.APT.CookieCutter has been used exclusively by this particular threat group
  • Finally, the command and control domain inform[.]bedircati[.]com seen in this activity was also used during the Clandestine Fox campaign

Another evolutionary step for this threat group is that they have diversified their tool usage with the use of the Kaba/PlugX/Sogu malware – something we have never seen them do before.

As we have noted in other blog posts, APT threat actors take advantage of every possible vector to try to gain a foothold in the organizations they target. Social networks are increasingly used for both personal and business reasons, and are one more potential threat vector that both end-users and network defenders need to think about.

Unfortunately, it is very common for users to let their guard down when using social networks or personal email, since they don’t always treat these services with the same level of risk as their work email.  As more companies allow their employees to telecommute, or even allow them to access company networks and/or resources using their personal computers, these attacks targeting their personal email addresses pose significant risk to the enterprise.

Acknowledgements

 The author would like to acknowledge the following colleagues for their contributions to this report: Josh Dennis, Mike Oppenheim, Ned Moran, and Joshua Homan.

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