How to implement APT32 sample analysis

1. Basic information

##Sample MD5bb3306543ff******* *9372bb3c72712Sample file size3.29 MB (3,449,856 bytes)Sample type Backdoor programSample descriptionUsing Office malicious macros to load Trojan modulesAnalysis timeDecember 2019

2. Analysis

2.1 Introduction

This malicious document has been implanted with three pieces of malicious macro code. The main function of the macro is to load and execute the malicious document in the memory. Shellcode code stored in hexadecimal stream mode.

The function of the ShellCode part is to extract a DLL Trojan program {A96B020F-0000-466F-A96D-A91BBF8EAC96}.dll from itself, and then execute the export function DllEntry of this Dll to release two 2 in the memory A DLL file related to network communication. The network communication related files are used to support HTTP, HTTPS and UDP protocol communication, and finally establish a communication connection with the C2 end to accept control instructions.

Note: {A96B020F-0000-466F-A96D-A91BBF8EAC96}.dll name is consistent with the DLL name of a previously analyzed APT32 sample, and the Shellcode code obfuscation method is similar, the memory loading method is similar, and the IOC extraction method is also similar. All belong to the APT32 organization, so this sample is judged to be related to APT32.

2.2 Deception execution

This attack uses malicious macro code to load malicious modules, and uses social engineering to disguise itself as 360 prompt information to gain the trust of users, thereby Trick users into enabling malicious macro code.

2.3 Malicious Macro Analysis

A total of three pieces of malicious macro code were implanted in this malicious document. The first piece of code is saved in the default location of office. 2. The third piece of malicious macro code is saved in the header of the document in the form of a hexadecimal stream.

The first macro code (the first macro code to be executed) reads the second macro code saved in the hexadecimal stream from the beginning of the document, dynamically loads and Call the entry function x_N0th2ngH3r3().

The second section of macro code reads the third section of macro code saved in the hexadecimal stream from the beginning of the document, dynamically loads and calls the entry function x_N0th2ngH3r3 ().

The third section of macro code loads the Shellcode code stored in the hexadecimal stream in the malicious document into the memory by creating a remote thread for the WINWORD process.

2.4 Shellcode Malicious Code Analysis

The core function of ShellCode is to extract a DLL file from itself, and self-load this DLL in the memory, and then Execute the exported function DllEntry of this dll. The picture below shows the corrected PE header data:

After dumping the Shellcode file from the memory, using LordPE you can see that the export name of the file is: {A96B020F-0000 -466F-A96D-A91BBF8EAC96}.dll. As shown below:

##2.5 Analysis of {A96B020F-0000-466F-A96D-A91BBF8EAC96}.dll

There is an encrypted resource in the decrypted DLL Resource file:

When the DLL is running, it first obtains the resource file and decrypts it. The decrypted resource file contains Trojan configuration information and two network communication-related DLL files, network communication related files are used to support HTTP, HTTPS and UDP protocol communication. The picture below shows the decrypted resource file information:

The data structure of the resource is as follows:

2.6 Communication Analysis

Passed by {A96B020F- The C2 domain name resolution address 45.122.138.31 decrypted from the 0000-466F-A96D-A91BBF8EAC96}.dll file resource establishes a communication connection, and uses the POST method in the HTTP protocol to send an online notification to the C2 end, and finally accepts the control end command of the C2 end. Control the target terminal.

2.7 Backdoor Function Analysis

Create Process

Create Directory, Delete Directory

File search, read and write, create, delete files and other operations

Registry read and write operations

2.8IOC

cloud.360cn.info

dns.chinanews.network

aliexpresscn.net

chinaport.org

3. Trend

APT32 is a Vietnamese hacker organization, also known as the OceanLotus organization , focused on attacking foreign companies with close ties to Vietnam, mainly attacking companies related to cybersecurity, manufacturing, media, banks, hotels, technology infrastructure, and consulting. The stolen information included trade secrets, confidential conversation logs, and progress plans. The attack method is to send well-designed phishing emails to targets, and include watering hole attacks with tempting malicious attachments in the emails to implant backdoors or malware into the targets to achieve the goal. The malicious document analyzed this time is the attachment in the phishing email received by the customer.

Through tracking research on the APT32 organization, we found that the organization has now begun to use cloud-based email analysis software in order to monitor and track the distribution of emails, and is gradually using the latest cutting-edge technology to achieve attack purposes. Practitioners in special industries should remain vigilant and confirm the legitimacy of the document when opening emails or sensitive information documents from unknown sources.

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