BLINDINGCAN - Malware Used by Lazarus -

In the previous article, we introduced one type of malware that Lazarus (also known as Hidden Cobra) uses after network intrusion. It is confirmed that this attack group uses multiple types of malware including BLINDINGCAN, which CISA recently introduced in its report [1].
This article summarises the result of our analysis on BLINDINGCAN.

BLINDINGCAN overview

The malware runs when a loader loads a DLL file. Figure 1 shows the flow of events until BLINDINGCAN runs. JPCERT/CC has confirmed that the DLL file is encoded in some samples (which requires decoding by the loader before execution).

BLINDINGCAN behaviour
Figure 1: BLINDINGCAN behaviour

BLINDINGCAN shares some features with the aforementioned malware including its function and communication encoding algorithm. The following sections will explain its configuration and communication protocol.

Configuration

The configuration of BLINDINGCAN(size: 0xA84) is stored in one of the following locations:

  • Hardcoded in the malware itself
  • Stored in a registry entry
  • Saved as a file

In case it is saved as a file, it is stored in the same folder where BLINDINGCAN is located. We have confirmed that the following directory is used if the configuration is stored in a registry entry.

Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion
Value: "SM_Dev16[numeric string]"

The configuration is encrypted using either XOR encoding, AES or RC4. The encryption key is either fixed or generated based on the environment of the infected device. JPCERT/CC has confirmed the following patterns of encryption keys:

  • [File name][Export function name][Service name]
  • [CPUID][Computer name][Processor name][Physical memory size]

Figure 2 shows an example of decoded configuration. This includes proxy information as well as C&C server information. (Please see Appendix A for details.)

Configuration example
Figure 2: Configuration example

Obfuscation

Some part of code in BLINDINGCAN is obfuscated using RC4. Figure 3 is an example of obfuscated code. The RC4 encryption key is hardcoded in the sample itself.

Obfuscation
Figure 3: Obfuscation

Communication with C&C server

Below is an example HTTP POST request data that BLINDINGCAN sends in the beginning.

POST /[PATH] HTTP/1.1
Connection: Keep-Alive
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded
Accept: */*
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) Chrome/28.0.1500.95 Safari/537.36
Host: [Server]
Content-Length: [Length]

id=d3Ztd3lod2t0Tqf42ux9uv3FGH+Y3oAc2w==&bbs=HA==&tbl=hzE4dlKcRq3gokgAGeMQug== &bbs_form=4GQAAA==

The format of the data is as follows. (All the values except for the RC4 key is RC4-encrypted and Base64-encoded.) The param2 in the first HTTP POST request is the encoded value of a string "T1B7D95256A2001E".

id=[RC4 key][param1:param2:param3]&[param1]=[Random value (between 1000 and 10000)]&[param2]=["T1B7D95256A2001E"]&[param3]=[Random binary data]

The parameters in the POST data (param1, param2, param3) are randomly selected from the below:

boardid,bbsNo,strBoardID,userid,bbs,filename,code,pid,seqNo,ReportID,v,PageNumber,num,view,read,action,page,mode,idx,cateId,bbsId,pType,pcode,index,tbl,idx_num,act,bbs_id,bbs_form,bid,bbscate,menu,tcode,b_code,bname,tb,borad01,borad02,borad03,mid,newsid,table,Board_seq,bc_idx,seq,ArticleID,B_Notice,nowPage,webid,boardDiv,sub_idxa

The RC4 encryption used here is different from the regular one. It has a process to shift the key stream for C00h times. The following is the RC4 encryption process written in Python. It does not apply to param3, which uses the regular RC4.

def custom_rc4(data, key):
    x = 0
    box = list(range(256))
    for i in range(256):
        x = (x + int(box[i]) + int(key[i % len(key)])) % 256
        box[i], box[x] = box[x], box[i]

    x = 0
    for i in range(0xC00):
        i = i + 1
        x = (x + int(box[i % 256])) % 256
        wow_x = x
        box[i % 256], box[x] = box[x], box[i % 256]
        wow_y = i % 256

    x = wow_y
    y = wow_x
    out = []
    for char in data:
        x = (x + 1) % 256
        y = (y + box[x]) % 256
        box[x], box[y] = box[y], box[x]
        out.append(chr(char ^ box[(box[x] + box[y]) % 256]))

    return ''.join(out)

Figure 4 is the flow of communication from the beginning of its communication with a C&C server until receiving commands.

BLINDINGCAN communication flow
Figure 4: BLINDINGCAN communication flow

If a Base64-encoded value of param3 ([Random binary data] in Figure 4) is received from the server as a response to the first request, the malware sends another request.
The next data is sent with empty param2 and a command request (Command request (0x2040) in Figure 4) in param3. (Please see Appendix B for the details of param3 format.) The data in param3 is XOR-encoded, RC4-encrypted and then Base64-encoded.
After that BLINDINGCAN receives a command from a C&C server. (The format of the response data is the same as param3. Please see Appendix B). The response data is also XOR-encoded, RC4-encrypted and Base64-encoded. The only difference is that the "+" sign is replaced by a space.

Commands

BLINDINGCAN performs multiple functions including the following. (Please see Appendix C for details.)

  • Operation on files (create a list, delete, move, modify timestamp, copy)
  • Operation on processes (create a list, execute, kill)
  • Upload/download files
  • Obtain disk information
  • Obtain a list of services
  • Execute arbitrary shell command

In closing

We have introduced two kinds of malware used by Lazarus so far. However, they are known to use other types of malware as well. We will provide an update if we observe any new kind of malware.
The C&C server information of the samples mentioned in the article are listed in Appendix D. Please make sure that none of your device is communicating with these hosts.

Shusei Tomonaga
(Translated by Yukako Uchida)

Reference

[1] CISA: Malware Analysis Report (AR20-232A)
https://us-cert.cisa.gov/ncas/analysis-reports/ar20-232a

Appendix A: Configuration

Table A: List of configurations
Offset Description Remarks
0x000 Number of C&C servers Up to 5
0x004 C&C server 1
0x108 C&C server 2
0x20C C&C server 3
0x310 C&C server 4
0x414 C&C server 5
0x518 Flag for proxy
0x51C Proxy IP address
0x520 Proxy port number
0x522 Flag for C&C reply
0x526 Flag for drive information
0x52A Flag for session information
0x52E Save configuration
0x532 Communication interval
0x534 Start time
0x53C seed Used when generating random data to send
0x59C File name File obtained by the command "0x2039"
0x5FC Unknown
0x65C Unknown
0x660 Not assigned
0x674 Execute process name Contains "c:¥windows¥system32¥cmd.exe"
0x87C Temp folder Command execution result is stored

Appendix B: Contents of data exchanged

Table B: Data format of param3 and response data
Offset Length Contents
0x00 2 Not assigned
0x02 2 Command
0x04 4 Not assigned
0x08 4 Parameter length
0x0C - Parameter (Base64 + RC4)

Appendix C: Commands

Table C: List of commands
Value Contents
0x2009 Get system information
0x2010 Get drive information
0x2011 Get directory list
0x2012 Execute command (Regular output)
0x2013 Upload file (compressed in zlib)
0x2014 Download file
0x2015 Execute process
0x2016 Execute process (CreateProcessAsUser)
0x2019 Get process list
0x2020 Kill process
0x2021 Delete file (sdelete)
0x2022 Check connection
0x2023 Change current directory
0x2027 Modify file creation time
0x2028 Change communication interval with C&C server
0x2029 End session with C&C server
0x2030 Uninstall
0x2031 Get configuration
0x2032 Overwrite configuration
0x2033 Get directory information
0x2034 Get drive available space
0x2037 -
0x2038 Sleep
0x2039 Get file name
0x2046 Write file
0x2048 Copy file
0x2049 Move file
0x2050 Delete file

Appendix D: C&C server

  • https://www.automercado.co.cr/empleo/css/main.jsp
  • https://www.curiofirenze.com/include/inc-site.asp
  • https://www.ne-ba.org/files/news/thumbs/thumbs.asp
  • https://www.sanlorenzoyacht.com/newsl/include/inc-map.asp

Appendix E: Sample hash value

  • 8db272ea1100996a8a0ed0da304610964dc8ca576aa114391d1be9d4c5dab02e
  • 58027c80c6502327863ddca28c31d352e5707f5903340b9e6ccc0997fcb9631d
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