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Magniber Ransomware Wants to Infect Only the Right People

Introduction


 

Exploit kit (EK) use has been on the decline since late 2016;
  however, certain activity remains consistent. The Magnitude Exploit
  Kit is one such example that continues to affect users, particularly
  in the APAC region.


 

In Figure 1, which is based on FireEye Dynamic threat Intelligence
  (DTI) reports shared in March 2017, we can see the regions affected by
  Magnitude EK activity during the last three months of 2016 and the
  first three months of 2017.


 


 
 
 Figure 1: Magnitude EK distribution as
    seen in March 2017


 

This trend continued until late September 2017, when we saw
  Magnitude EK focus primarily on the APAC region, with a large chunk
  targeting South Korea. Magnitude EK activity then fell off the radar
  until Oct. 15, 2017, when it came back and began focusing solely on
  South Korea. Previously it had been distributing Cerber ransomware,
  but Cerber distribution has declined (we have also seen a decline of
  Cerber being distributed via email) and now it is distributing
  ransomware known as Magniber. 


 

Infection


 

The first reappearance of Magnitude EK on Oct. 15 came as a
  malvertising redirection from the domain: fastprofit[.]loan. The
  infection chain is shown in Figure 2.


 


 
 
 Figure 2: Infection chain


 

The Magnitude EK landing page consisted of CVE-2016-0189, which was
  first reported by FireEye as being used in     href="https://www.fireeye.com/blog/threat-research/2016/07/exploit_kits_quickly.html">Neutrino
    Exploit Kit after it was patched. Figure 3 shows the landing
  page and CVE usage.


 


 
 
 Figure 3: Magnitude EK landing page


 

As seen previously with Magnitude EK, the payload is downloaded as a
  plain EXE (see Figure 4) and domain infrastructure is hosted on the
  following server:


 

“Apache/2.2.15 (CentOS) DAV/2 mod_fastcgi/2.4.6”


 


 
 
 Figure 4: Magnitude payload header and
    plain MZ response


 

Payload


 

In the initial report     href="http://blog.trendmicro.com/trendlabs-security-intelligence/magnitude-exploit-kit-now-targeting-korea-with-magniber-ransomware/">published
    by our colleagues at Trend Micro, the ransomware being
  distributed is referred to as Magniber. These ransomware payloads only
  seem to target Korean systems, since they won’t execute if the system
  language is not Korean.


 

Magniber encrypts user data using the AES128. The sample used
  (dc2a2b84da359881b9df1ec31d03c715) for this analysis was pulled from
  our DTI system when the campaign was active. Of note, this sample
  differs from the hash shared publically by Trend Micro, but the two
  exhibit the same behavior and share the infection vector, and both
  were distributed around the same time.


 

The malware contains a binary payload in its resource section
  encrypted in reverse using RC4. It starts unpacking it from the end of
  the buffer to its start. Reverse RC4 decryption keys are 30 bytes long
  and also contain non-ASCII characters. They are as follows:


 
  • dc2a2b84da359881b9df1ec31d03c715 RC4 key:
    • { 0x6b,
              0xfe, 0xc4, 0x23, 0xac, 0x50, 0xd7, 0x91, 0xac, 0x06, 0xb0,
              0xa6, 0x65, 0x89, 0x6a, 0xcc, 0x05, 0xba, 0xd7, 0x83, 0x04,
              0x90, 0x2a, 0x93, 0x8d, 0x2d, 0x5c, 0xc7, 0xf7, 0x3f }

    •    

 

The malware calls GetSystemDefaultUILanguage, and if the
  system language is not Korean, it exits (instructions can be seen in
  Figure 5). After unpacking in memory, the malware starts executing the
  unpacked payload.


 


 
 
 Figure 5: Language check targeted at Korea


 

A mutex with name "ihsdj" is created to prevent multiple
  executions. The payload then generates a pseudorandom 19-character
  string based on the CPU clock from multiple GetTickCount calls.
  The string is then used to create a file in the user’s %TEMP%
  directory (e.g. "xxxxxxxxxxxxxxxxxxx.ihsdj"), which contains
  the IV (Initialization Vector) for the AES128 encryption and a copy of
  the malware itself with the name "ihsdj.exe".


 

Next, the malware constructs 4 URLs for callback. It uses the
  19-character long pseudorandom string it generated, and the following
  domains to create the URLs:


 
  • bankme.date
  • jobsnot.services

  •  
  • carefit.agency
  • hotdisk.world

 

In order to evade sandbox systems, the malware checks to see if it's
  running inside a VM and appends the result to the URL callback. It
  does this by sandwiching and executing CPUID instructions (shown in
  Figure 6) between RDTSC calls, forcing VMEXIT.


 


 
 
 Figure 6: CPUID instruction to detect VM presence


 

The aforementioned VM check is done multiple times to gather the
  average execution time of the CPUID, and if the average execution time
  is greater than 1000, it considers the system to be a VM. In case the
  test fails and the malware thinks the system is a VM, a "1"
  is appended at the end of the URL (see Figure 7); otherwise,
  "0" is appended. The format of the URL is as follows:


 
  • http://[19 character pseudorandom string].[callback
        domain]/new[0 or 1]

 

Examples of this would be:


 
  • http://7o12813k90oggw10277.bankme[.]date/new1

  •  
  • http://4bg8l9095z0287fm1j5.bankme[.]date/new0

 


 
 
 Figure 7: Command and control communication


 

If the malware is executed a second time after encryption, the
  callback URL ends in "end0" or "end1" instead of
  "new". An example of this would be:


 
  • hxxp://j2a3y50mi0a487230v1.bankme[.]date/end1

 

The malware then starts to encrypt user files on the system,
  renaming them by adding a ".ihsdj" extension to the end. The
  AES128 Key and IV for the sample analyzed are listed:


 
  • IV: EP866p5M93wDS513
  • AES128 Key:
      S25943n9Gt099y4K

 

A text file "READ_ME_FOR_DECRYPT_xxxxxxxxxxxxxxxxxxx_.txt"
  is created in the user’s %TEMP% directory and shown to the user. The
  ransom message is shown in Figure 8.


 


 
 
 Figure 8: Ransom message for the infected user


 

The malware also adds scheduled tasks to run its copy from %TEMP%
  with compatibility assistant, and loads the user message as follows:


 
  • schtasks /create /SC MINUTE /MO 15 /tn ihsdj /TR
        "pcalua.exe -a %TEMP%\ihsdj.exe
  • schtasks /create /SC
        MINUTE /MO 15 /tn xxxxxxxxxxxxxxxxxxx /TR
      %TEMP%\READ_ME_FOR_DECRYPT_xxxxxxxxxxxxxxxxxxx_.txt

 

The malware then issues a command to delete itself after exiting,
  using the following local ping to provide delay for the deletion:


 
  • cmd /c ping localhost -n 3 > nul & del
      C:\PATH\MALWARE.EXE)

 

Figure 9 contains the Python code for unpacking the malware payload,
  which is encrypted using RC4 in reverse.


 


 
 
 Figure 9: Python script for unpacking
    malware payload


 

Conclusion


 

Ransomware is a significant threat to enterprises. While the current
  threat landscape suggests a large portion of attacks are coming from
  emails, exploit kits continue to put users at risk – especially those
  running old software versions and not using ad blockers. Enterprises
  need to make sure their network nodes are fully patched.


 

All FireEye products detect the malware in our MVX engine.
  Additionally,     href="https://www.fireeye.com/products/nx-network-security-products.html">FireEye
  NX blocks delivery at the infection point.


 

IOCs


 
Malware Sample Hash

 
  • dc2a2b84da359881b9df1ec31d03c715 (decryption key shared)

 
Malverstiser Domains

 
  • fastprofit[.]loan
  • fastprofit[.]me

 
EK Domain Examples

 
  • 3e37i982wb90j.fileice[.]services

  •  
  • a3co5a8iab2x24g90.helpraw[.]schule

  •  
  • 2i1f3aadm8k.putback[.]space

 
Command and Control Domains

 
  • 3ee9fuop6ta4d6d60bt.bankme.date

  •  
  • 3ee9fuop6ta4d6d60bt.jobsnot.services

  •  
  • 3ee9fuop6ta4d6d60bt.carefit.agency

  •  
  • 3ee9fuop6ta4d6d60bt.hotdisk.world

Source: Magniber Ransomware Wants to Infect Only the Right People

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