Thirty years ago today, Netscape Communications and Sun Microsystems issued a joint press release announcing JavaScript, an object scripting language designed for creating interactive web applications. The language emerged from a frantic 10-day sprint at pioneering browser company Netscape, where engineer Brendan Eich hacked together a working internal prototype during May 1995.
While the JavaScript language didn’t ship publicly until that September and didn’t reach a 1.0 release until March 1996, the descendants of Eich’s initial 10-day hack now run on approximately 98.9 percent of all websites with client-side code, making JavaScript the dominant programming language of the web. It’s wildly popular; beyond the browser, JavaScript powers server backends, mobile apps, desktop software, and even some embedded systems. According to several surveys, JavaScript consistently ranks among the most widely used programming languages in the world.
In crafting JavaScript, Netscape wanted a scripting language that could make webpages interactive, something lightweight that would appeal to web designers and non-professional programmers. Eich drew from several influences: The syntax looked like a trendy new programming language called Java to satisfy Netscape management, but its guts borrowed concepts from Scheme, a language Eich admired, and Self, which contributed JavaScript’s prototype-based object model.
Security and developer teams are scrambling to address a highly critical security flaw in frameworks tied to the popular React JavaScript library. Not only is the vulnerability, which also is in the Next.js framework, easy to exploit, but React is widely used, including in 39% of cloud environments.
If you can navigate a nested IF function, manage thousands of rows of data, or troubleshoot the dreaded #REF! error in Microsoft Excel, congratulations—you've been programming for years without even knowing it.
As a language, JavaScript receives more than its fair share of criticism. Its default global variables, prototypical inheritance, and dynamic typing are often considered flaws that can lead to sloppy code. But I’m here to defend JavaScript, not as the ideal language, but as a great choice for beginners.
Tsundere is a new botnet, discovered by our Kaspersky GReAT around mid-2025. We have correlated this threat with previous reports from October 2024 that reveal code similarities, as well as the use of the same C2 retrieval method and wallet. In that instance, the threat actor created malicious Node.js packages and used the Node Package Manager (npm) to deliver the payload. The packages were named similarly to popular packages, employing a technique known as typosquatting. The threat actor targeted libraries such as Puppeteer, Bignum.js, and various cryptocurrency packages, resulting in 287 identified malware packages. This supply chain attack affected Windows, Linux, and macOS users, but it was short-lived, as the packages were removed and the threat actor abandoned this infection method after being detected.
The threat actor resurfaced around July 2025 with a new threat. We have dubbed it the Tsundere bot after its C2 panel. This botnet is currently expanding and poses an active threat to Windows users.
Initial infection
Currently, there is no conclusive evidence on how the Tsundere bot implants are being spread. However, in one documented case, the implant was installed via a Remote Monitoring and Management (RMM) tool, which downloaded a file named pdf.msi from a compromised website. In other instances, the sample names suggest that the implants are being disseminated using the lure of popular Windows games, particularly first-person shooters. The samples found in the wild have names such as “valorant”, “cs2”, or “r6x”, which appear to be attempts to capitalize on the popularity of these games among piracy communities.
Malware implants
According to the C2 panel, there are two distinct formats for spreading the implant: via an MSI installer and via a PowerShell script. Implants are automatically generated by the C2 panel (as described in the Infrastructure section).
MSI installer
The MSI installer was often disguised as a fake installer for popular games and other software to lure new victims. Notably, at the time of our research, it had a very low detection rate.
The installer contains a list of data and JavaScript files that are updated with each new build, as well as the necessary Node.js executables to run these scripts. The following is a list of files included in the sample:
The last three files in the list are legitimate Node.js files. They are installed alongside the malicious artifacts in the user’s AppData\Local\nodejs directory.
An examination of the CustomAction table reveals the process by which Windows Installer executes the malware and installs the Tsundere bot:
This will execute Node.js code that spawns a new Node.js process, which runs the loader JavaScript code (in this case, B4jHWzJnlABB2B7). The resulting child process runs in the background, remaining hidden from the user.
Loader script
The loader script is responsible for ensuring the correct decryption and execution of the main bot script, which handles npm unpackaging and configuration. Although the loader code, similar to the code for the other JavaScript files, is obfuscated, it can be deobfuscated using open-source tools. Once executed, the loader attempts to locate the unpackaging script and configuration for the Tsundere bot, decrypts them using the AES-256 CBC cryptographic algorithm with a build-specific key and IV, and saves the decrypted files under different filenames.
The configuration file is a JSON that defines a directory and file structure, as well as file contents, which the malware will recreate. The malware author refers to this file as “config”, but its primary purpose is to package and deploy the Node.js package manager (npm) without requiring manual installation or downloading. The unpackaging script is responsible for recreating this structure, including the node_modules directory with all its libraries, which contains packages necessary for the malware to run.
With the environment now set up, the malware proceeds to install three packages to the node_modules directory using npm:
ws: a WebSocket networking library
ethers: a library for communicating with Ethereum
pm2: a Node.js process management tool
Loader script installing the necessary toolset for Tsundere persistence and execution
The pm2 package is installed to ensure the Tsundere bot remains active and used to launch the bot. Additionally, pm2 helps achieve persistence on the system by writing to the registry and configuring itself to restart the process upon login.
PowerShell infector
The PowerShell version of the infector operates in a more compact and simplified manner. Instead of utilizing a configuration file and an unpacker — as done with the MSI installer — it downloads the ZIP file node-v18.17.0-win-x64.zip from the official Node.js website nodejs[.]org and extracts it to the AppData\Local\NodeJS directory, ultimately deploying Node.js on the targeted device. The infector then uses the AES-256-CBC algorithm to decrypt two large hexadecimal-encoded variables, which correspond to the bot script and a persistence script. These decrypted files, along with a package.json file are written to the disk. The package.json file contains information about the malicious Node.js package, as well as the necessary libraries to be installed, including the ws and ethers packages. Finally, the infector runs both scripts, starting with the persistence script that is followed by the bot script.
The PowerShell infector creates a package file with the implant dependencies
Persistence is achieved through the same mechanism observed in the MSI installer: the script creates a value in the HKCU:\Software\Microsoft\Windows\CurrentVersion\Run registry key that points to itself. It then overwrites itself with a new script that is Base64 decoded. This new script is responsible for ensuring the bot is executed on each login by spawning a new instance of the bot.
Tsundere bot
We will now delve into the Tsundere bot, examining its communication with the command-and-control (C2) server and its primary functionality.
C2 address retrieval
Web3 contracts, also known as smart contracts, are deployed on a blockchain via transactions from a wallet. These contracts can store data in variables, which can be modified by functions defined within the contract. In this case, the Tsundere botnet utilizes the Ethereum blockchain, where a method named setString(string _str) is defined to modify the state variable param1, allowing it to store a string. The string stored in param1 is used by the Tsundere botnet administrators to store new WebSocket C2 servers, which can be rotated at will and are immutable once written to the Ethereum blockchain.
The Tsundere botnet relies on two constant points of reference on the Ethereum blockchain:
In order to change the C2 server, the Tsundere botnet makes a transaction to update the state variable with a new address. Below is a transaction made on August 19, 2025, with a value of 0 ETH, which updates the address.
Smart contract containing the Tsundere botnet WebSocket C2
The state variable has a fixed length of 32 bytes, and a string of 24 bytes (see item [2] in the previous image) is stored within it. When this string is converted from hexadecimal to ASCII, it reveals the new WebSocket C2 server address: ws[:]//185.28.119[.]179:1234.
To obtain the C2 address, the bot contacts various public endpoints that provide remote procedure call (RPC) APIs, allowing them to interact with Ethereum blockchain nodes. At the start of the script, the bot calls a function named fetchAndUpdateIP, which iterates through a list of RPC providers. For each provider, it checks the transactions associated with the contract address and wallet owner, and then retrieves the string from the state variable containing the WebSocket address, as previously observed.
Malware code for retrieval of C2 from the smart contract
The Tsundere bot verifies that the C2 address starts with either ws:// or wss:// to ensure it is a valid WebSocket URL, and then sets the obtained string as the server URL. But before using this new URL, the bot first checks the system locale by retrieving the culture name of the machine to avoid infecting systems in the CIS region. If the system is not in the CIS region, the bot establishes a connection to the server via a WebSocket, setting up the necessary handlers for receiving, sending, and managing connection states, such as errors and closed sockets.
Bot handlers for communication
Communication
The communication flow between the client (Tsundere bot) and the server (WebSocket C2) is as follows:
The Tsundere bot establishes a WebSocket connection with the retrieved C2 address.
An AES key is transmitted immediately after the connection is established.
The bot sends an empty string to confirm receipt of the key.
The server then sends an IV, enabling the use of encrypted communication from that point on.
Encryption is required for all subsequent communication.
The bot transmits the OS information of the infected machine, including the MAC address, total memory, GPU information, and other details. This information is also used to generate a unique identifier (UUID).
The C2 server responds with a JSON object, acknowledging the connection and confirming the bot’s presence.
With the connection established, the client and server can exchange information freely.
To maintain the connection, keep-alive messages are sent every minute using ping/pong messages.
The bot sends encrypted responses as part of the ping/pong messages, ensuring continuous communication.
Tsundere communication process with the C2 via WebSockets
The connections are not authenticated through any additional means, making it possible for a fake client to establish a connection.
As previously mentioned, the client sends an encrypted ping message to the C2 server every minute, which returns a pong message. This ping-pong exchange serves as a mechanism for the C2 panel to maintain a list of currently active bots.
Functionality
The Tsundere bot is designed to allow the C2 server to send dynamic JavaScript code. When the C2 server sends a message with ID=1 to the bot, the message is evaluated as a new function and then executed. The result of this operation is sent back to the server via a custom function named serverSend, which is responsible for transmitting the result as a JSON object, encrypted for secure communication.
Tsundere bot evaluation code once functions are received from the C2
The ability to evaluate code makes the Tsundere bot relatively simple, but it also provides flexibility and dynamism, allowing the botnet administrators to adapt it to a wide range of actions.
However, during our observation period, we did not receive any commands or functions from the C2 server, possibly because the newly connected bot needed to be requested by other threat actors through the botnet panel before it could be utilized.
Infrastructure
The Tsundere bot utilizes WebSocket as its primary protocol for establishing connections with the C2 server. As mentioned earlier, at the time of writing, the malware was communicating with the WebSocket server located at 185.28.119[.]179, and our tests indicated that it was responding positively to bot connections.
The following table lists the IP addresses and ports extracted from the provided list of URLs:
IP
Port
First seen (contract update)
ASN
185.28.119[.]179
1234
2025-08-19
AS62005
196.251.72[.]192
1234
2025-08-03
AS401120
103.246.145[.]201
1234
2025-07-14
AS211381
193.24.123[.]68
3011
2025-06-21
AS200593
62.60.226[.]179
3001
2025-05-04
AS214351
Marketplace and control panel
No business is complete without a marketplace, and similarly, no botnet is complete without a control panel. The Tsundere botnet has both a marketplace and a control panel, which are integrated into the same frontend.
Tsundere botnet panel login
The notable aspect of Tsundere’s control panel, dubbed “Tsundere Netto” (version 2.4.4), is that it has an open registration system. Any user who accesses the login form can register and gain access to the panel, which features various tabs:
Bots: a dashboard displaying the number of bots under the user’s control
Settings: user settings and administrative functions
Build: if the user has an active license, they can create new bots using the two previously mentioned methodologies (MSI or PowerShell)
Market: this is the most interesting aspect of the panel, as it allows users to promote their individual bots and offer various services and functionalities to other threat actors. Each build can create a bot that performs a specific set of actions, which can then be offered to others
Monero wallet: a wallet service that enables users to make deposits or withdrawals
Socks proxy: a feature that allows users to utilize their bots as proxies for their traffic
Tsundere botnet control panel, building system and market
Each build generates a unique build ID, which is embedded in the implant and sent to the C2 server upon infection. This build ID can be linked to the user who created it. According to our research and analysis of other URLs found in the wild, builds are created through the panel and can be downloaded via the URL:
At the time of writing this, the panel typically has between 90 and 115 bots connected to the C2 server at any given time.
Attribution
Based on the text found in the implants, we can conclude with high confidence that the threat actor behind the Tsundere botnet is likely Russian-speaking. The use of the Russian language in the implants is consistent with previous attacks attributed to the same threat actor.
Russian being used throughout the code
Furthermore, our analysis suggests a connection between the Tsundere botnet and the 123 Stealer, a C++-based stealer available on the shadow market for $120 per month. This connection is based on the fact that both panels share the same server. Notably, the main domain serves as the frontend for the 123 Stealer panel, while the subdomain “idk.” is used for the Tsundere botnet panel.
123 Stealer C2 panel sharing Tsundere’s infrastructure and showcasing its author
By examining the available evidence, we can link both threats to a Russian-speaking threat actor known as “koneko”. Koneko was previously active on a dark web forum, where they promoted the 123 Stealer, as well as other malware, including a backdoor. Although our analysis of the backdoor revealed that it was not directly related to Tsundere, it shared similarities with the Tsundere botnet in that it was written in Node.js and used PowerShell or MSI as infectors. Before the dark web forum was seized and shut down, koneko’s profile featured the title “node malware senior”, further suggesting their expertise in Node.js-based malware.
Conclusion
The Tsundere botnet represents a renewed effort by a presumably identified threat actor to revamp their toolset. The Node.js-based bot is an evolution of an attack discovered in October of last year, and it now features a new strategy and even a new business model. Infections can occur through MSI and PowerShell files, which provides flexibility in terms of disguising installers, using phishing as a point of entry, or integrating with other attack mechanisms, making it an even more formidable threat.
Additionally, the botnet leverages a technique that is gaining popularity: utilizing web3 contracts, also known as “smart contracts”, to host command-and-control (C2) addresses, which enhances the resilience of the botnet infrastructure. The botnet’s possible author, koneko, is also involved in peddling other threats, such as the 123 Stealer, which suggests that the threat is likely to escalate rather than diminish in the coming months. As a result, it is essential to closely monitor this threat and be vigilant for related threats that may emerge in the near future.
Cryptocurrency wallets Note: These are wallets that have changed the C2 address in the smart contract since it was created.
0x73625B6cdFECC81A4899D221C732E1f73e504a32
0x10ca9bE67D03917e9938a7c28601663B191E4413
0xEc99D2C797Db6E0eBD664128EfED9265fBE54579
0xf11Cb0578EA61e2EDB8a4a12c02E3eF26E80fc36
0xdb8e8B0ef3ea1105A6D84b27Fc0bAA9845C66FD7
0x10ca9bE67D03917e9938a7c28601663B191E4413
0x52221c293a21D8CA7AFD01Ac6bFAC7175D590A84
0x46b0f9bA6F1fb89eb80347c92c9e91BDF1b9E8CC
The modern development world is almost entirely dependent on third-party modules. While this certainly speeds up development, it also creates a massive attack surface for end users, since anyone can create these components. It is no surprise that malicious modules are becoming more common. When a single maintainer account for popular modules or a single popular dependency is compromised, it can quickly turn into a supply chain attack. Such compromises are now a frequent attack vector trending among threat actors. In the last month alone, there have been two major incidents that confirm this interest in creating malicious modules, dependencies, and packages. We have already discussed the recent compromise of popular npm packages. September 16, 2025 saw reports of a new wave of npm package infections, caused by the self-propagating malware known as Shai-Hulud.
Shai-Hulud is designed to steal sensitive data, expose private repositories of organizations, and hijack victim credentials to infect other packages and spread on. Over 500 packages were infected in this incident, including one with more than two million weekly downloads. As a result, developers who integrated these malicious packages into their projects risk losing sensitive data, and their own libraries could become infected with Shai-Hulud. This self-propagating malware takes over accounts and steals secrets to create new infected modules, spreading the threat along the dependency chain.
Technical details
The worm’s malicious code executes when an infected package is installed. It then publishes infected releases to all packages the victim has update permissions for.
Once the infected package is installed from the npm registry on the victim’s system, a special command is automatically executed. This command launches a malicious script over 3 MB in size named bundle.js, which contains several legitimate, open-source work modules.
Key modules within bundle.js include:
Library for interacting with AWS cloud services
GCP module that retrieves metadata from the Google Cloud Platform environment
Functions for TruffleHog, a tool for scanning various data sources to find sensitive information, specifically secrets
Tool for interacting with the GitHub API
The JavaScript file also contains network utilities for data transfer and the main operational module, Shai-Hulud.
The worm begins its malicious activity by collecting information about the victim’s operating system and checking for an npm token and authenticated GitHub user token in the environment. If a valid GitHub token is not present, bundle.js will terminate. A distinctive feature of Shai-Hulud is that most of its functionality is geared toward Linux and macOS systems: almost all malicious actions are performed exclusively on these systems, with the exception of using TruffleHog to find secrets.
Exfiltrating secrets
After passing the checks, the malware uses the token mentioned earlier to get information about the current GitHub user. It then runs the extraction function, which creates a temporary executable bash script at /tmp/processor.sh and runs it as a separate process, passing the token as an argument. Below is the extraction function, with strings and variable names modified for readability since the original source code was illegible.
The extraction function, formatted for readability
The bash script is designed to communicate with the GitHub API and collect secrets from the victim’s repository in an unconventional way. First, the script checks if the token has the necessary permissions to create branches and work with GitHub Actions. If it does, the script gets a list of all the repositories the user can access from 2025. In each of these, it creates a new branch named shai-hulud and uploads a shai-hulud-workflow.ymlworkflow, which is a configuration file for describing GitHub Actions workflows. These files are automation scripts that are triggered in GitHub Actions whenever changes are made to a repository. The Shai-Hulud workflow activates on every push.
The malicious workflow configuration
This file collects secrets from the victim’s repositories and forwards them to the attackers’ server. Before being sent, the confidential data is encoded twice with Base64.
This unusual method for data collection is designed for a one-time extraction of secrets from a user’s repositories. However, it poses a threat not only to Shai-Hulud victims but also to ordinary researchers. If you search for “shai-hulud” on GitHub, you will find numerous repositories that have been compromised by the worm.
Open GitHub repositories compromised by Shai-Hulud
The main bundle.js script then requests a list of all organizations associated with the victim and runs the migration function for each one. This function also runs a bash script, but in this case, it saves it to /tmp/migrate-repos.sh, passing the organization name, username, and token as parameters for further malicious activity.
The bash script automates the migration of all private and internal repositories from the specified GitHub organization to the user’s account, making them public. The script also uses the GitHub API to copy the contents of the private repositories as mirrors.
We believe these actions are intended for the automated theft of source code from the private repositories of popular communities and organizations. For example, the well-known company CrowdStrike was caught in this wave of infections.
The worm’s self-replication
After running operations on the victim’s GitHub, the main bundle.js script moves on to its next crucial stage: self-replication. First, the script gets a list of the victim’s 20 most downloaded packages. To do this, it performs a search query with the username from the previously obtained npm token:
Next, for each of the packages it finds, it calls the updatePackage function. This function first attempts to download the tarball version of the package (a .TAR archive). If it exists, a temporary directory named npm-update-{target_package_name} is created. The tarball version of the package is saved there as package.tgz, then unpacked and modified as follows:
The malicious bundle.js is added to the original package.
A postinstall command is added to the package.json file (which is used in Node.js projects to manage dependencies and project metadata). This command is configured to execute the malicious script via node bundle.js.
The package version number is incremented by 1.
The modified package is then re-packed and published to npm as a new version with the npm publish command. After this, the temporary directory for the package is cleared.
The updatePackage function, formatted for readability
Uploading secrets to GitHub
Next, the worm uses the previously mentioned TruffleHog utility to harvest secrets from the target system. It downloads the latest version of the utility from the original repository for the specific operating system type using the following link:
The worm also uses modules for AWS and Google Cloud Platform (GCP) to scan for secrets. The script then aggregates the collected data into a single object and creates a repository named “Shai-Hulud” in the victim’s profile. It then uploads the collected information to this repository as a data.json file.
Below is a list of data formats collected from the victim’s system and uploaded to GitHub:
A distinctive characteristic of the modified packages is that they contain an archive named package.tar. This is worth noting because packages usually contain an archive with a name that matches the package itself.
Through our research, we were able to identify the first package from which Shai-Hulud began to spread, thanks to a key difference. As we mentioned earlier, after infection, a postinstall command to execute the malicious script, node bundle.js, is written to the package.json file. This command typically runs immediately after installation. However, we discovered that one of the infected packages listed the same command as a preinstall command, meaning it ran before the installation. This package was ngx-bootstrap version 18.1.4. We believe this was the starting point for the spread of this infection. This hypothesis is further supported by the fact that the archive name in the first infected version of this package differed from the name characteristic of later infected packages (package.tar).
While investigating different packages, we noticed that in some cases, a single package contained multiple versions with malicious code. This was likely possible because the infection spread to all maintainers and contributors of packages, and the malicious code was then introduced from each of their accounts.
Infected libraries and CrowdStrike
The rapidly spreading Shai-Hulud worm has infected many popular libraries that organizations and developers use daily. Shai-Hulud has infected over 500 popular packages in recent days, including libraries from the well-known company CrowdStrike.
Among the infected libraries were the following:
But the event that has drawn significant attention to this spreading threat was the infection of the @ctrl/tinycolor library, which is downloaded by over two million users every week.
As mentioned above, the malicious script exposes an organization’s private repositories, posing a serious threat to their owners, as this creates a risk of exposing the source code of their libraries and products, among other things, and leading to an even greater loss of data.
Prevention and protection
To protect against this type of infection, we recommend using a specialized solution for monitoring open-source components. Kaspersky maintains a continuous feed of compromised packages and libraries, which can be used to secure your supply chain and protect development from similar threats.
For personal devices, we recommend Kaspersky Premium, which provides multi-layered protection to prevent and neutralize infection threats. Our solution can also restore the device’s functionality if it’s infected with malware.
For corporate devices, we advise implementing a comprehensive solution like Kaspersky Next, which allows you to build a flexible and effective security system. This product line provides threat visibility and real-time protection, as well as EDR and XDR capabilities for investigation and response. It is suitable for organizations of any scale or industry.
Kaspersky products detect the Shai-Hulud threat as HEUR:Worm.Script.Shulud.gen.
In the event of a Shai-Hulud infection, and as a proactive response to the spreading threat, we recommend taking the following measures across your systems and infrastructure:
Use a reliable security solution to conduct a full system scan.
Audit your GitHub repositories:
Check for repositories named shai-hulud.
Look for non-trivial or unknown branches, pull requests, and files.
Audit GitHub Actions logs for strings containing shai-hulud.
Reissue npm and GitHub tokens, cloud keys (specifically for AWS and Google Cloud Platform), and rotate other secrets.
Clear the cache and inventory your npm modules: check for malicious ones and roll back versions to clean ones.
Check for indicators of compromise, such as files in the system or network artifacts.