ESET researchers have discovered Hodur, a previously undocumented Korplug variant spread by Mustang Panda, that uses phishing lures referencing current events in Europe, including the invasion of Ukraine

ESET researchers discovered a still-ongoing campaign using a previously undocumented Korplug variant, which they named Hodur due to its resemblance to the THOR variant previously documented by Unit 42 in 2020. In Norse mythology, Hodur is Thor’s blind half-brother, who is tricked by Loki into killing their half-brother Baldr.

Key findings in this blogpost:

  • As of March 2022, this campaign is still ongoing and goes back to at least August 2021.
  • Known victims include research entities, internet service providers, and European diplomatic missions.
  • The compromise chain includes decoy documents that are frequently updated and relate to events in Europe.
  • The campaign uses a custom loader to execute a new Korplug variant.
  • Every stage of the deployment process utilizes anti-analysis techniques and control-flow obfuscation, which sets it apart from other campaigns.
  • ESET researchers provide an in-depth analysis of the capabilities and commands of this new variant.

Victims of this campaign are likely lured with phishing documents abusing the latest events in Europe such as Russia’s invasion of Ukraine. This resulted in more than three million residents fleeing the war to neighboring countries, leading to an unprecedented crisis on Ukraine’s borders. One of the filenames related to this campaign is Situation at the EU borders with Ukraine.exe.

Other phishing lures mention updated COVID-19 travel restrictions, an approved regional aid map for Greece, and a Regulation of the European Parliament and of the Council. The last one is a real document available on the European Council’s website. This shows that the APT group behind this campaign is following current affairs and is able to successfully and swiftly react to them.

Figure 1. Countries affected by Mustang Panda in this campaign

Affected countries:

  • Mongolia
  • Vietnam
  • Myanmar
  • Greece
  • Russia
  • Cyprus
  • South Sudan
  • South Africa

Affected verticals:

  • Diplomatic missions
  • Research entities
  • Internet service providers (ISP)

Analysis

Based on code similarities and the many commonalities in Tactics, Techniques, and Procedures (TTPs), ESET researchers attribute this campaign with high confidence to Mustang Panda (also known as TA416, RedDelta, or PKPLUG). It is a cyberespionage group mainly targeting governmental entities and NGOs. Its victims are mostly, but not exclusively, located in East and Southeast Asia with a focus on Mongolia. The group is also known for its campaign targeting the Vatican in 2020.

While we haven’t been able to identify the verticals of all victims, this campaign seems to have the same targeting objectives as other Mustang Panda campaigns. Following the APT’s typical victimology, most victims are located in East and Southeast Asia, along with some in European and African countries. According to ESET telemetry, the vast majority of targets are located in Mongolia and Vietnam, followed by Myanmar, with only a few in the other affected countries.

Mustang Panda’s campaigns frequently use custom loaders for shared malware including Cobalt Strike, Poison Ivy, and Korplug (also known as PlugX). The group has also been known to create its own Korplug variants. Compared to other campaigns using Korplug, every stage of the deployment process utilizes anti-analysis techniques and control-flow obfuscation.

This blogpost contains a detailed analysis of this previously unseen Korplug variant used in this campaign. This activity is part of the same campaign recently covered by Proofpoint, but we provide additional historical and targeting information.

Toolset

Mustang Panda is known for its elaborate custom loaders and Korplug variants, and the samples used in this campaign showcase this perfectly.

Compromise chains seen in this campaign follow the typical Korplug pattern: a legitimate, validly signed, executable vulnerable to DLL search-order hijacking, a malicious DLL, and an encrypted Korplug file are deployed on the target machine. The executable is abused to load the module, which then decrypts and executes the Korplug RAT. In some cases, a downloader is used first to deploy these files along with a decoy document. This process is illustrated in Figure 2.

Figure 2. Overview of the deployment process for the Hodur Korplug variant.

What sets this campaign apart is the heavy use of control-flow obfuscation and anti-analysis techniques at every stage of the deployment process. The following sections describe the behavior of each stage and take a deeper look at the defense evasion techniques used in each of them.

Initial access

We haven’t been able to observe the initial deployment vector, but our analysis points to phishing and watering hole attacks as likely vectors. In instances where we saw a downloader, the filenames used suggest a document with an interesting subject for the target. Such examples include:

  • COVID-19 travel restrictions EU reviews list of third countries.exe
  • State_aid__Commission_approves_2022-2027_regional_aid_map_for_Greece.exe
  • REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL.exe
  • Situation at the EU borders with Ukraine.exe

To further the illusion, these binaries download and open a document that has the same name but with a .doc or .pdf extension. The contents of these decoys accurately reflect the filename. As shown in Figure 3, at least one of them is a publicly accessible legitimate document from the European Parliament.

Figure 3. First page of the decoy document for the REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL.exe downloader. It’s a real document available on the European Council’s website.

Downloader

Although its complexity has increased over the course of the campaign, the downloader is fairly straightforward. This increase in complexity comes from additional anti-analysis techniques, which we cover later in this section.

It first downloads four files over HTTPS: a decoy document, a legitimate executable, a malicious module and an encrypted Korplug file. The combination of those last three components to execute a payload via DLL side-loading is sometimes referred to as a trident and is a technique commonly used by Mustang Panda, and with Korplug loaders in general. Both the server addresses and file paths are hardcoded in the downloader executable. Once everything is downloaded, and the decoy document opened to distract the victim, the downloader uses the following command line to launch the legitimate executable:

cmd /c ping 8.8.8.8 -n 70&&”%temp%\<legitimate executable>”

This ping command both checks internet connectivity and introduces a delay (through the -n 70 option) before executing the downloaded, legitimate executable.

The downloader uses multiple anti-analysis techniques, many of which are also used in the loader and final payload. Additional obfuscation has been added to new versions over the course of the campaign without otherwise changing their goal.

In early versions of the downloader, junk code and opaque predicates were used to hinder analysis, as shown in Figure 4, but the server and filenames are plainly visible in cleartext.

Figure 4. Control flow obfuscation in early versions of the downloader

In later versions, the files on the server are RC4 encrypted, using the base 10 string representation of the file size as the key, and then hex-encoded. This process is illustrated in the Python snippet below. The opposite operations are performed client-side by the downloader to recover the plaintext files. This is likely done to bypass network-level protections.

from Crypto.cipher import ARC4
key = “%d” % len(plaintext)
rc4 = ARC4.new(key)
cipher_content = rc4.encrypt(plaintext).hex().upper()

These versions replace the use of cleartext strings with encrypted stack strings. They are still hardcoded in the file, but the obfuscation surrounding them, and the use of different keys, makes it hard to decrypt them statically in an automated manner. This same technique is used heavily in the subsequent stages. Encrypted stack strings are also used to obfuscate calls to Windows API functions.

First, the name of the target function is decrypted and passed to a function. This function obtains a pointer to the InMemoryOrderModuleList field of the PEB (Process Environment Block). It then iterates over the loaded modules, passing each handle to GetProcAddress along with the function name until the target function is successfully resolved. Part of this process can be seen in Figure 5.

Figure 5. Obfuscation of Windows API calls in the downloader. The screenshot shows a call to WriteFile, but the same pattern is used for all API functions.

Loader

As is common with Korplug, the loader is a DLL that exploits a side-loading vulnerability in a legitimate, signed executable. We have observed many different applications being abused in this campaign, for instance a vulnerable SmadAV executable previously seen by Qurium in a campaign attributed to Mustang Panda that targeted Myanmar.

The loader exports multiple functions. The exact list varies depending on the abused application, but in all cases, only one of them does anything of consequence. In all of the loaders we observed, this is the exported function with the highest load address. All the other exports, and the library’s entry point, either return immediately or execute some do-nothing junk code. Many of these exports have names that consist of random lowercase letters and point to the same address as shown in Table 1.

Table 1. Functions exported by a Hodur loader. The createSystemFontsUsingEDL export is the one that loads the final malware stage in this version.

Name Ordinal Function RVA
CreatePotPlayerExW 1 0x00007894
RunPotPlayer 2 0x000166A5
createSystemFontsUsingEDL 3 0x00016779
gGegcerhwyvxtkrtyawvugo 4 0x00007894
liucigvyworf 5 0x00007639
ojohjinbgdfqtcwxojeusoneslciyxtiyjuieaugadjpd 6 0x000077CA
soeevhiywsypipesxfhgxboleahfwvlqcqp 7 0x00007894
srkeqffanuhiuwahbmatdurggpffhbkcpukyxgxmosn 8 0x00007894
thggvmrv 9 0x00007701

The loader function obtains the directory from which the DLL is running using GetModuleFileNameA and tries to open the encrypted Korplug file it contains. That filename is hardcoded in the loader. It reads the file’s contents into a locally allocated buffer and decrypts it. The loader makes this buffer executable using VirtualProtect before calling into it at offset 0x00.

Windows API function calls are obfuscated with a different technique than that used in the downloader. Unlike the loader, which contains the names of its functions (as shown in Table 1 above), only the 64-bit hashes of the Windows API function calls are present in the binary. To resolve those functions, the loader traverses the export lists of all loaded libraries via the InMemoryOrderModuleList of the PEB. Each export’s name is hashed, then compared to the expected value. The FNV-1a hash algorithm, recently brought back into the mainstream by the Sunburst backdoor, has previously been used by Mustang Panda, in Korplug loaders documented by XORHEX, to resolve GetProcAddress and LoadLibraryA, although it was not identified by name in that analysis. In this version, however, it is used for all API functions.

Korplug backdoor

Korplug (also known as PlugX) is a RAT used by multiple APT groups. In spite of it being so widely used, or perhaps because of it, few reports extensively describe its commands and the data it exfiltrates. Its functionality is not constant between variants, but there does seem to exist a significant overlap in the list of commands between the version we analyzed and other sources such as the Avira report from January 2020 and the plugxdecoder project on GitHub.

As previously mentioned, the variant used in this campaign bears many similarities to the THOR variant, which is why we have named it Hodur. The similarities include the use of the Software\CLASSES\ms-pu registry key, the same format for C&C servers in the configuration, and use of the Static window class.

As expected for Korplug payloads, this stage is only ever decrypted in memory by the loader. Only the encrypted version is written to disk in a file with a .dat extension.

Unless stated otherwise, all hardcoded strings discussed in this section are stored as encrypted stack strings.

In this module, Windows API functions are obfuscated through a combination of the methods used in previous stages. LoadLibraryA and GetProcAddress are resolved via the FNV-1a hashing technique and stack strings are decrypted and passed to them to obtain the target function.

Loading

Once decrypted, the payload is a valid DLL that exports a single function. In almost all observed samples from this campaign, this function is named StartProtect. However, launching it directly via this export or its entry point will not execute the main payload and the loading process is quite intricate.

As explained in the previous section, the file is decrypted in memory as a continuous blob by the loader and the execution starts at offset 0x00. The PE header contains shellcode, shown in Figure 6, that calls a specific offset that corresponds to the module’s single export.

Figure 6. Shellcode in the PE header that calls the exported function

This function parses the PE blob in memory and manually maps it as a library into a newly allocated buffer. This includes mapping the various sections, resolving imports and, finally, using DLL_PROCESS_ATTACH to call the DLL entry point. Once again, opaque predicates and junk code are used to obfuscate the purpose of this function.

The entry point of the properly loaded library is then called with the non-standard value of 0x04 for the fdwReason parameter (only values from 0x00 to 0x03 are currently defined). This special value is required to get it to execute its main payload. This simple check prevents the RAT from being trivially executed directly with a generic tool like rundll32.exe.

The backdoor first decrypts its configuration using the string 123456789 as a repeating XOR key. Once decrypted, the configuration block starts with ########. The layout of the configuration varies slightly between samples, but they all contain at least the following fields:

  • Installation directory name. Also used as the name of the registry key created for persistence. This value roughly corresponds to the name of the abused application with three random letters appended (e.g., FontEDLZeP or AdobePhotosGQp)
  • Mutex name
  • A value that is either a version or ID string
  • List of C&C servers. Each entry includes IP address, port number, and a number indicating the protocol to use with that C&C

The backdoor then checks the path from which it is running using GetModuleFileNameW. If this matches %userprofile%\<installation directory> or %allusersprofile%\<installation directory>, the RAT functionality will be executed. Otherwise, it will go through the installation process.

Installation

To install itself, the malware creates the aforementioned directory under %allusersprofile%. Using SetFileAttributesW, it is then marked as hidden and system. The vulnerable executable, loader module, and encrypted Korplug files are copied to the new directory.

Next, persistence is established. Earlier samples achieved this by creating a scheduled task to be run at boot via schtasks.exe. Newer samples add a registry entry to Software\Microsoft\Windows\CurrentVersion\Run, trying the HKLM hive first, then HKCU. This entry has the same name as the installation directory with its value set to the newly copied executable’s path.

Once persistence has been set up, the malware launches the executable from its new location and exits.

RAT

The RAT functionality of the Hodur variant used in this campaign mostly lines up with other Korplug variants, with some additional commands and characteristics. As we have previously stated, though, detailed analyses of Korplug commands are few and far between, so we aim to provide such an analysis in the hopes of aiding future analysts.

When in this mode, the backdoor iterates through the list of C&C servers in its configuration until it reaches the end or receives an Uninstall command. For each of those servers, it processes commands until it receives a Stop command or encounters an error.

Hodur’s initial handshake can be done over HTTPS or TCP. This is determined by a value in the configuration for that particular C&C server. Subsequent communication is always done over TCP using a custom protocol that we describe in this section, along with the commands that can be issued. Hodur uses sockets from the Windows Sockets API (Winsock) that support overlapped I/O.

Following the initial handshake, Hodur’s communications involve TCP messages that consist of a header, with the structure described in Table 2, followed by a message body that is usually compressed using LZNT1 and always encrypted with RC4. Messages whose Command number header field have the 0x10000000 bit set (those that contain file contents for the ReadFile and WriteFile commands, described in Table 3) have encrypted but not compressed message bodies. All encrypted message bodies use the hardcoded key [email protected]#L$PH% with a four-byte random nonce (the value at offset 0x00 in the header) appended to it.

Table 2. Header format used for communication between the C&C and the backdoor

Offset Field Description
0x00 Nonce Random nonce appended to the RC4 key.
0x04 Command number This field indicates the command to run or the command that caused this response to be sent.
0x08 Length of body Length of the message body. It seems that this field isn’t checked by the client for messages from the C&C server.
0x0C Command exit status The return or error value of the command that was run. This field is not checked by the client in messages received from the C&C server.

Hodur’s C&C message headers are transmitted in the clear, followed by variably sized (the value at offset 0x08 of the header) message bodies. The format of the message body varies per command, but once decrypted and decompressed, values of variable length (like strings) are always at a message body’s end and their offset in the body is stored as an integer in the corresponding message field.

Like the version described by Avira, Hodur has two groups of commands – 0x1001 and 0x1002 – each with its own handler. The C&C server can set which group to listen for by sending the corresponding ID as the command number when a client is not already in one of the two modes. It will continue to listen for the same group until it receives the Stop command, or an error occurs (including receiving a message with an invalid Command number in its header).

The first group, 0x1001, contains commands for managing the execution of the backdoor and doing initial reconnaissance on a newly compromised host. As these commands take no arguments, messages sent by the C&C server consist only of the headers. Table 3 contains a list of these commands. The GetSystemInfo command is described in more detail below. Note that no command names are present in the RAT; they were either taken from previous analyses or provided by us.

Table 3. Commands in group 0x1001

ID Name Description Data in client response
0x1000 Ping Sent by the client when it starts listening for commands from this group. Between 0 and 64 random bytes
0x1001 GetSystemInfo Get information about the system. See Table 4
0x1002 ListenThread Start a new thread that listens for group 0x1002 commands. None
0x1004 ResetConnection Terminate with WSAECONNRESET. N/A
0x1005 Uninstall Delete persistence registry keys, remove itself and created folders. None
0x1007 Stop Set registry key System\CurrentControlSet\Control\‌Network\allow to 1 and exit. N/A

The GetSystemInfo command collects extensive information about the system, as detailed in Table 4. If it doesn’t already exist, the Software\CLASSES\ms-pu\CLSID registry key is set to the current timestamp, trying HKLM first then HKCU. The value of this key is then sent in the response.

Table 4. Response body format for the GetSystemInfo response

Offset Value Offset Value
0x00 Magic bytes 0x20190301 0x38 Suite mask
0x04 Client IP address of the C&C socket 0x3A Product type
0x08 Server IP address of the C&C socket 0x3C 0x01 if the process is running as WOW64
0x0C RAM in KB 0x40 System time – year
0x10 CPU clock rate in MHz 0x42 System time – month
0x14 Display width in pixels 0x44 Timestamp of first run (offset)
0x18 Display height in pixels 0x46 Service pack version string (offset)
0x1C Default locale 0x48 Unknown
0x20 Current tick count 0x4A Username (offset)
0x24 OS major version 0x4C Computer name (offset)
0x28 OS minor version 0x4E Mutex name (offset)
0x2C OS build number 0x50 Unknown
0x30 OS platform ID 0x52 List of machine IP addresses (offset)
0x34 Service pack major version 0x54 Always two 0x00 bytes
0x36 Service pack minor version

The 0x1002 group contains commands that provide RAT functionality, as detailed in Table 5. Some of these take parameters provided in the command’s message body. The FindFiles command is described in more detail below. Again, note that no command names are present in the RAT; they were either taken from previous analyses or provided by us.

Table 5. Commands in group 0x1002

ID Name Description Data in C&C request Data in client response
0x1002 Ping Sent by the client when it starts listening for commands from this group. N/A None
0x3000 ListDrives List all mapped drives (A: to Z:) and their properties.

All 26 entries are sent back in one message body. Drives that aren’t present have all fields set to 0x00.

None · Drive type
· Total size
· Space available to user
· Free space
· Volume name (offset)
· File system name (offset)
0x3001 ListDirectory List the contents of the specified directory. The client sends one response message per entry. Directory path · Is a directory?
· File attributes
· File size
· Creation time
· Last write time
· Filename (offset)
· 8.3 filename (offset)
0x3002 Sent by the client when it has finished executing the ListDirectory command. N/A None
0x3004 ReadFile Read a file in chunks of 0x4000 bytes. · Creation time
· Last access time
· Last write time
· Has offset
· Offset in file
· File size
· File path
0x10003005 Chunk of read file data. N/A Read data
0x10003006 Sent by the client when it has finished executing the ReadFile command. N/A None
0x3007 WriteFile Write to a file and restore previous timestamp.

Creates parent directories if they don’t exist.

· Creation time
· Last access time
· Last write time
· Has offset
· Offset in file
· File path (offset)
None
0x10003008 Sent by the server with data to write to the file. Data to write N/A
0x10003009 Sent by the server when the WriteFile operation is complete. None N/A
0x300A CreateDirectory Create a directory. Directory path None
0x300B CanReadFile Try to open a file with read permissions. File path None
0x300C DesktopExecute Execute a command on a hidden desktop. Command line to execute PROCESS_INFORMATION structure for the created process.
0x300D FileOperation Perform a file operation using SHFileOperation. · wFunc
· fFlags
· pFrom (offset)
· pTo (offset)
None
0x300E GetEnvValue Get the value of an environment variable. Environment variable Environment variable value.
0x300F CreateProgramDataDir Creates the directory %SYSTEM%\ProgramData, optionally with a subdirectory. Subdirectory relative path (optional) None
0x3102 FindFiles Recursively search a directory for files matching a given pattern. · Starting directory
· Search pattern
See response body format in Table 6.
0x7002 RemoteShell Start an interactive remote cmd.exe session. None None
0x7003 Result of the last command run. N/A Command output

FindFiles command

Starting from the provided directory, this command searches for files whose names match the given pattern. This pattern supports the same wildcard characters as the Windows FindFirstFile API. For each matching file, the client sends a response message with its body in the format described in Table 6.

Table 6. Format of the response body for the FindFiles command

Offset Value Offset Value
0x00 File attributes 0x24 Folder path (offset)
0x04 File size in bytes 0x26 Filename (offset)
0x0C Creation time 0x28 8.3 filename (offset)
0x1C Last write time

One response message with an empty body is sent once the search is completed.

Conclusion

The decoys used in this campaign show once more how quickly Mustang Panda is able to react to world events. For example, an EU regulation on COVID-19 was used as a decoy only two weeks after it came out, and documents about the war in Ukraine started being used in the days following the beginning of the launch of the invasion. This group also demonstrates an ability to iteratively improve its tools, including its signature use of trident downloaders to deploy Korplug.

For any inquiries about our research published on WeLiveSecurity, please contact us at [email protected]

ESET Research now also offers private APT intelligence reports and data feeds. For any inquiries about this service, visit the ESET Threat Intelligence page.

IoCs

SHA-1 Filename ESET detection name Description
69AB6B9906F8DCE03B43BEBB7A07189A69DC507B coreclr.dll Win32/Agent.ADMW Korplug loader.
10AE4784D0FFBC9CD5FD85B150830AEA3334A1DE N/A Win32/Korplug.TC Decrypted Korplug (dumped from memory).
69AB6B9906F8DCE03B43BEBB7A07189A69DC507B coreclr.dll Win32/Agent.ADMW Korplug loader.
4EBFC035179CD72D323F0AB357537C094A276E6D PowerDVD18.exe Win32/Delf.UTN Korplug loader.
FDBB16B8BA7724659BAB5B2E1385CFD476F10607 N/A Win32/Korplug.TB Decrypted Korplug (dumped from memory).
7E059258CF963B95BDE479D1C374A4C300624986 N/A Win32/Korplug.TC Decrypted Korplug (dumped from memory).
7992729769760ECAB37F2AA32DE4E61E77828547 SHELLSEL.ocx Win32/Agent.ADMW Korplug loader.
F05E89D031D051159778A79D81685B62AFF4E3F9 SymHp.exe Win32/Delf.UTN Korplug loader.
AB01E099872A094DC779890171A11764DE8B4360 BoomerangLib.dll Win32/Korplug.TH Korplug loader.
CDB15B1ED97985D944F883AF05483990E02A49F7 PotPlayer.dll Win32/Agent.ADYO Korplug loader.
908F55D21CCC2E14D4FF65A7A38E26593A0D9A70 SmadHook32.dll Win32/Agent.ADMW Korplug loader.
477A1CE31353E8C26A8F4E02C1D378295B302C9E N/A Win32/Agent.ADMW Korplug loader.
52288C2CDB5926ECC970B2166943C9D4453F5E92 SmadHook32c.dll Win32/Agent.ADMW Korplug loader.
CBD875EE456C84F9E87EC392750D69A75FB6B23A SHELLSEL.ocx Win32/Agent.ADMW Korplug loader.
2CF4BAFE062D38FAF4772A7D1067B80339C2CE82 Adobe_Caps.dll Win32/Agent.ADMW Korplug loader.
97C92ADD7145CF9386ABD5527A8BCD6FABF9A148 DocConvDll.dll Win32/Agent.ADYO Korplug loader.
39863CECA1B0F54F5C063B3015B776CDB05971F3 N/A Win32/Korplug.TD Decrypted Korplug (dumped from memory).
0D5348B5C9A66C743615E819AEF152FB5B0DAB97 FontEDL.exe clean Vulnerable legitimate Font File Generator executable.
C8F5825499315EAF4B5046FF79AC9553E71AD1C0 Silverlight.Configuration.exe clean Vulnerable legitimate Microsoft Silverlight Configuration Utility executable.
D4FFE4A4F2BD2C19FF26139800C18339087E39CD PowerDVDLP.exe clean Vulnerable legitimate PowerDVD executable.
65898ACA030DCEFDA7C970D3A311E8EA7FFC844A Symantec.exe clean Vulnerable legitimate Symantec AntiVirus executable.
7DDB61872830F4A0E6BF96FAF665337D01F164FC Adobe Stock Photos CS3.exe clean Vulnerable legitimate Adobe Stock Photos executable.
C13D0D669365DFAFF9C472E615A611E058EBF596 COVID-19 travel restrictions EU reviews list of third countries.exe Win32/Agent_AGen.NJ Downloader.
062473912692F7A3FAB8485101D4FCF6D704ED23 REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL.exe Win32/TrojanDownloader.Agent.GDL Downloader.
2B5D6BB5188895DA4928DD310C7C897F51AAA050 log.dll Win32/Agent.ACYW Korplug loader.
511DA645A7282FB84FF18C33398E67D7661FD663 2.exe Win32/Agent.ADPL Korplug loader.
59002E1A58065D7248CD9D7DD62C3F865813EEE6 log.dll Win32/Agent.ADXE Korplug loader.
F67C553678B7857D1BBC488040EA90E6C52946B3 KINGSTON.exe Win32/Agent.ADXZ Korplug Loader.
58B6B5FD3F2BFD182622F547A93222A4AFDF4E76 PotPlayer.exe clean Vulnerable legitimate executable.

Network

Domain IP First seen Notes
103.56.53[.]120 2021‑06‑15 Korplug C&C
154.204.27[.]181 2020‑10‑05 Korplug C&C.
43.254.218[.]42 2021‑02‑09 Download server.
45.131.179[.]179 2020‑10‑05 Korplug C&C.
176.113.69[.]91 2021-04-19 Korplug C&C.
upespr[.]com 45.154.14[.]235 2022-01-17 Download server.
urmsec[.]com 156.226.173[.]23 2022‑02‑23 Download server.
101.36.125[.]203 2021-06-01 Korplug C&C.
185.207.153[.]208 2022‑02‑03 Download server.
154.204.27[.]130 2021-12-14 Korplug C&C.
92.118.188[.]78 2022-01-27 Korplug C&C.
zyber-i[.]com 107.178.71[.]211 2022-03-01 Download server.
locvnpt[.]com 103.79.120[.]66 2021-05-21 Download server. This domain was previously used in a 2020 campaign documented by Recorded Future.

MITRE ATT&CK techniques

This table was built using version 10 of the MITRE ATT&CK framework.

Tactic ID Name Description
Resource Development T1583.001 Acquire Infrastructure: Domains Mustang Panda has registered domains for use as download servers.
T1583.003 Acquire Infrastructure: Virtual Private Server Some download servers used by Mustang Panda appear to be on shared hosting.
T1583.004 Acquire Infrastructure: Server Mustang Panda uses servers that appear to be exclusive to the group.
T1587.001 Develop Capabilities: Malware Mustang Panda has developed custom loader and Korplug versions.
T1588.006 Obtain Capabilities: Vulnerabilities Multiple DLL hijacking vulnerabilities are used in the deployment process.
T1608.001 Stage Capabilities: Upload Malware Malicious payloads are hosted on the download servers.
Execution T1059.003 Command and Scripting Interpreter: Windows Command Shell Windows command shell is used to execute commands sent by the C&C server.
T1106 Native API Mustang Panda uses CreateProcess and ShellExecute for execution.
T1129 Shared Modules Mustang Panda uses LoadLibrary to load additional DLLs at runtime. The loader and RAT are DLLs.
T1204.002 User Execution: Malicious File Mustang Panda relies on the user executing the initial downloader.
T1574.002 Hijack Execution Flow: DLL Side-Loading The downloader obtains and launches a vulnerable application so it loads and executes the malicious DLL that contains the second stage.
Persistence T1547.001 Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder Korplug can persist via registry Run keys.
T1053.005 Scheduled Task/Job: Scheduled Task Korplug can persist by creating a scheduled task that runs on startup.
Defense Evasion T1140 Deobfuscate/Decode Files or Information The Korplug file is encrypted and only decrypted at runtime, and its configuration data is encrypted with XOR.
T1564.001 Hide Artifacts: Hidden Files and Directories Directories created during the installation process are set as hidden system directories.
T1564.003 Hide Artifacts: Hidden Window Korplug can run commands on a hidden desktop. Multiple hidden windows are used during the deployment process.
T1070 Indicator Removal on Host Korplug’s uninstall command deletes registry keys that store data and provide persistence.
T1070.004 Indicator Removal on Host: File Deletion Korplug can remove itself and all created directories.
T1070.006 Indicator Removal on Host: Timestomp When writing to a file, Korplug sets the file’s timestamps to their previous values.
T1036.004 Masquerading: Masquerade Task or Service Scheduled tasks created for persistence use legitimate-looking names.
T1036.005 Masquerading: Match Legitimate Name or Location File and directory names match expected values for the legitimate app that is abused by the loader.
T1112 Modify Registry Korplug can create, modify, and remove registry keys.
T1027 Obfuscated Files or Information Some downloaded files are encrypted and stored as hexadecimal strings.
T1027.005 Obfuscated Files or Information: Indicator Removal from Tools Imports are hidden by dynamic resolution of API function names.
T1055.001 Process Injection: Dynamic-link Library Injection Some versions of the Korplug loader inject the Korplug DLL into a newly launched process.
T1620 Reflective Code Loading Korplug parses and loads itself into memory.
Discovery T1083 File and Directory Discovery Korplug can list files and directories along with their attributes and content.
T1082 System Information Discovery Korplug collects extensive information about the system including uptime, Windows version, CPU clock rate, amount of RAM and display resolution.
T1614 System Location Discovery Korplug retrieves the system locale using GetSystemDefaultLCID.
T1016 System Network Configuration Discovery Korplug collects the system hostname and IP addresses.
T1016.001 System Network Configuration Discovery: Internet Connection Discovery The downloader pings Google’s DNS server to check internet connectivity.
T1033 System Owner/User Discovery Korplug obtains the current user’s username.
T1124 System Time Discovery Korplug uses GetSystemTime to retrieve the current system time.
Collection T1005 Data from Local System Korplug collects extensive data about the system it’s running on.
T1025 Data from Removable Media Korplug can collect metadata and content from all mapped drives.
T1039 Data from Network Shared Drive Korplug can collect metadata and content from all mapped drives.
Command and Control T1071.001 Application Layer Protocol: Web Protocols Korplug can make the initial handshake over HTTPS.
T1095 Non-Application Layer Protocol C&C communication is done over a custom TCP-based protocol.
T1573.001 Encrypted Channel: Symmetric Cryptography C&C communication is encrypted using RC4.
T1008 Fallback Channels The Korplug configuration contains fallback C&C servers.
T1105 Ingress Tool Transfer Korplug can download additional files from the C&C server.
T1571 Non-Standard Port When Hodur performs its initial handshake over HTTPS, it uses the same port (specified in the configuration) as for the rest of the communication.
T1132.001 Data Encoding: Standard Encoding Korplug compresses transferred data using LZNT1.
Exfiltration T1041 Exfiltration Over C2 Channel Data exfiltration is done via the same custom protocol used to send and receive commands.