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Spear Phishing Techniques Used in Attacks Targeting the Mongolian Government

Introduction

 

FireEye recently observed a sophisticated campaign targeting
  individuals within the Mongolian government. Targeted individuals that
  enabled macros in a malicious Microsoft Word document may have been
  infected with     href="https://www.fireeye.com/content/dam/fireeye-www/global/en/current-threats/pdfs/rpt-poison-ivy.pdf">Poison
  Ivy, a popular remote access tool (RAT) that has been used for
  nearly a decade for key logging, screen and video capture, file
  transfers, password theft, system administration, traffic relaying,
  and more. The threat actors behind this attack demonstrated some
  interesting techniques, including:


 

  1.     Customized evasion based on victim profile – The campaign
        used a publicly available technique to evade AppLocker application
        whitelisting applied to the targeted systems.

  2.     Fileless execution and persistence – In targeted campaigns,
        threat actors often attempt to avoid writing an executable to the
        disk to avoid detection and forensic examination. The campaign we
        observed used four stages of PowerShell scripts without writing the
        the payloads to individual files.

  3.     Decoy documents – This campaign used PowerShell to download
        benign documents from the Internet and launch them in a separate
        Microsoft Word instance to minimize user suspicion of malicious
      activity.

 
Attack Cycle

 

The threat actors used social engineering to convince users to run
  an embedded macro in a Microsoft Word document that launched a
  malicious PowerShell payload.


 

The threat actors used two publicly available techniques, an
  AppLocker whitelisting bypass and a script to inject shellcode into
  the userinit.exe process. The malicious payload was spread across
  multiple PowerShell scripts, making its execution difficult to trace.
  Rather than being written to disk as individual script files, the
  PowerShell payloads were stored in the registry.   


 

Figure 1 shows the stages of the payload execution from the
  malicious macro.


 


 


 


  Figure 1: Stages of payload execution used in
    this attack


 
Social Engineering and Macro-PowerShell Level 1 Usage

 

Targets of the campaign received Microsoft Word documents via email
  that claimed to contain instructions for logging into webmail or
  information regarding a state law proposal.


 

When a targeted user opens the malicious document, they are
  presented with the messages shown in Figure 2, asking them to enable macros.


 


 


 


  Figure 2: Lure suggesting the user to enable
    Macros to see content


 
Bypassing Application Whitelisting Script Protections (AppLocker)

 

Microsoft application whitelisting solution AppLocker prevents
  unknown executables from running on a system. In April 2016, a
  security researcher demonstrated a way to bypass this using
  regsvr32.exe, a legitimate Microsoft executable permitted to execute
  in many AppLocker policies. The regsvr32.exe executable can be used to
  download a Windows Script Component file (SCT file) by passing the URL
  of the SCT file as an argument. This technique bypasses AppLocker
  restrictions and permits the execution of code within the SCT file.


 

We observed implementation of this bypass in the macro code to
  invoke regsvr32.exe, along with a URL passed to it which was hosting a
  malicious SCT file, as seen in Figure 3.


 


 


 


  Figure 3:  Command after de-obfuscation to
    bypass AppLocker via regsv32.exe


 

Figure 4 shows the entire command line parameter used to bypass AppLocker.


 


 


 


  Figure 4: Command line parameter used to bypass AppLocker


 

We found that the malicious SCT file invokes WScript to launch
  PowerShell in hidden mode with an encoded command, as seen in Figure 5.


 


 


 


  Figure 5: Content of SCT file containing code to
    launch encoded PowerShell


 
Decoding SCT: Decoy launch and Stage Two PowerShell

 

After decoding the PowerShell command, we observed another layer of
  PowerShell instructions, which served two purposes:


 

1.     There was code to download a decoy document from the Internet
  and open it in a second winword.exe process using the Start-Process
  cmdlet. When the victim enables macros, they will see the decoy
  document shown in Figure 6. This document contains the content
  described in the spear phishing email.


 


 


 


  Figure 6: Decoy downloaded and launched on the
    victim’s screen


 

2.     After launching the decoy document in the second winword.exe
  process, the PowerShell script downloads and runs another PowerShell
  script named f0921.ps1 as shown in Figure 7.


 


 


 


  Figure 7: PowerShell to download and run decoy
    decoy document and third-stage payload


 
Third Stage PowerShell Persistence

 

The third stage PowerShell script configures an encoded PowerShell
  command persistently as base64 string in the HKCU:
  \Console\FontSecurity registry key. Figure 8 shows a portion of the
  PowerShell commands for writing this value to the registry.


 


 


 


  Figure 8: Code to set registry with encoded
    PowerShell script


 

Figure 9 shows the registry value containing encoded PowerShell code
  set on the victims’ system.


 


 


 


  Figure 9: Registry value containing encoded
    PowerShell script


 

Figure 10 shows that using Start-Process, PowerShell decodes this
  registry and runs the malicious code.


 


 


 


  Figure 10: Code to decode and run malicious
    content from registry


 

The third stage PowerShell script also configures another registry
  value  named HKCU\CurrentVersion\Run\SecurityUpdate to launch the
  encoded PowerShell payload stored in the HKCU: \Console\FontSecurity
  key. Figure 11 shows the code for these actions. This will execute the
  PowerShell payload when the user logs in to the system.


 


 


 


  Figure 11: PowerShell registry persistence


 
Fourth Stage PowerShell Inject-LocalShellCode

 

The HKCU\Console\FontSecurity registry contains the fourth stage
  PowerShell script, shown decoded in Figure 12. This script borrows
  from the publicly available Inject-LocalShellCode PowerShell script
  from   href="https://github.com/PowerShellMafia/PowerSploit/blob/master/CodeExecution/Invoke-Shellcode.ps1">PowerSploit
  to inject shellcode.


 


 


 


  Figure 12: Code to inject shellcode


 
Shellcode Analysis

 

The shellcode has a custom XOR based decryption loop that uses a
  single byte key (0xD4), as seen in Figure 13.


 


 


 


  Figure 13: Decryption loop and call to decrypted shellcode


 

After the shellcode is decrypted and run, it injects a Poison Ivy
  backdoor into the userinit.exe as shown in Figure 14.


 


 


 


  Figure 14: Code injection in userinit.exe and
    attempt to access Poison Ivy related DAT files


 

In the decrypted shellcode, we also observed content and
  configuration related to Poison Ivy.  Correlating these bytes to the
  standard configuration of Poison Ivy, we can observe the following:


 
  • Active setup – StubPath
  • Encryption/Decryption key -
      version2013
  • Mutex name - 20160509                 

 

The Poison Ivy configuration dump is shown in Figure 15.


 


 


 


  Figure 15: Poison Ivy configuration dump


 
Conclusion

 

Although Poison Ivy has been a proven threat for some time, the
  delivery mechanism for this backdoor uses recent publicly available
  techniques that differ from previously observed campaigns. Through the
  use of PowerShell and publicly available security control bypasses and
  scripts, most steps in the attack are performed exclusively in memory
  and leave few forensic artifacts on a compromised host.


 

FireEye HX Exploit Guard is a behavior-based solution that is not
  affected by the tricks used here. It detects and blocks this threat at
  the initial level of the attack cycle when the malicious macro
  attempts to invoke the first stage PowerShell payload. HX also
  contains generic detections for the registry persistence, AppLocker
  bypasses and subsequent stages of PowerShell abuse used in this attack.


Source: Spear Phishing Techniques Used in Attacks Targeting the Mongolian Government

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