Attack Chain

1. Initial Access: A developer installs a malicious npm package (e.g., buffer-utilities), mistaking it for a legitimate or related package due to brandjacking techniques like suffix addition, version mimicry, or embedding legitimate code.
2. Dropper Execution: Upon installation or execution, the malicious package's embedded JavaScript code runs, decoding Base64-encoded URLs pointing to external payload servers.
3. Payload Fetching: The malicious code initiates an outbound network connection, typically from a Node.js process, to download additional payloads from command-and-control infrastructure (e.g., www.jsonkeeper.com).
4. Second-Stage Backdoor Deployment: The downloaded Node.js backdoor executes, performing host reconnaissance by collecting system information such as hostname, username, operating system, home directory, and active process arguments.
5. Command and Control (C2) Communication: The Node.js backdoor establishes persistent communication with its C2 server to retrieve configuration data and report collected telemetry back to the attackers.
6. Persistence & Third-Stage Payload: Following C2 instructions, the backdoor creates a hidden .vscode directory in the user's home folder, downloads further files (including f.js and a malicious package.json), and executes npm install --silent to fetch dependencies before launching f.js as a detached background process.
7. Ongoing Control & Updates: The deployed payload includes an update mechanism, allowing it to periodically reconnect to the C2 server, check for newer payload versions, and replace local files, ensuring continuous attacker access and control over the infected system.

Impact

This campaign represents a critical supply chain threat, particularly for organizations relying on the npm ecosystem for software development. Successful compromise means developers' systems are backdoored, potentially leading to intellectual property theft, credential compromise, further network intrusion, and disruption of development pipelines. The Node.js backdoor functions as a persistent staging framework, allowing the Lazarus Group to deploy additional malicious code and maintain long-term control. While specific victim counts are not disclosed, the wide reach of npm and the reported download numbers (up to 500 weekly for some packages) suggest a broad potential impact across various sectors.

Recommendation

• Deploy the Sigma rule "Detect Node.js Process Connecting to www.jsonkeeper.com" to your SIEM to identify direct C2 communication.
• Implement the Sigma rule "Detect npm install --silent Execution" to flag automated and potentially malicious package installations.
• Block network connections to www.jsonkeeper.com at the perimeter firewall or DNS resolver, as listed in the IOCs section.
• Organizations that installed packages associated with Sonatype-2026-003558 (e.g., buffer-utilities version 1.0.0) should remove them and treat affected hosts as potentially compromised.
• Investigate compromised systems for evidence of second-stage payload execution, hidden .vscode directories containing suspicious files like f.js or package.json, and any unusual process activity.