Njlogger

Overview

Spyware:Win32/Njlogger is a highly prevalent keylogging component, frequently encountered as a module embedded within the notorious **njRAT (Bladabindi)** remote access trojan, though it can occasionally be deployed standalone. Its primary function is the systematic, stealthy collection of user credentials, sensitive communications, and intellectual property by recording every keystroke made on the infected endpoint.

Understanding Njlogger
To an end-user, Njlogger operates entirely invisibly in the background. Passwords typed into web browsers, SSH clients, or corporate VPN portals are silently captured. For an enterprise, Njlogger represents a catastrophic breach of confidentiality. The stolen credentials can be used for immediate lateral movement, privilege escalation, or sold on dark web marketplaces to other Initial Access Brokers (IABs).

Execution and Data Collection Mechanics
Njlogger is typically deployed after an initial compromise (via phishing or exploit). Upon execution, it establishes persistence, often via the Registry Run keys or the Startup folder (`T1547.001`). The core functionality relies on API hooking, specifically the `SetWindowsHookEx` API (`T1056.001`). By hooking the keyboard message stream globally, Njlogger intercepts the `WH_KEYBOARD_LL` (low-level keyboard hook) event, capturing every keystroke before the intended application receives it. In addition to keystrokes, Njlogger frequently monitors the active window title (`GetForegroundWindow`) to provide context to the captured keys (e.g., showing that 'password123' was typed into 'Google Chrome - Bank Login'). It also frequently polls the system clipboard (`T1115`) to steal copied passwords. The collected data is written to a hidden, encrypted log file in the `%Temp%` or `%AppData%` directory before being exfiltrated to the botmaster (`T1048.003`).

Indicators of Compromise & Impact
The impact is total compromise of user credentials and sensitive data. Host-based IoCs include EDR alerts for suspicious processes employing API hooking (`SetWindowsHookEx`), the presence of rapidly growing, obfuscated `.log` or `.dat` files in user directories, and processes reading the clipboard excessively. Network IoCs involve regular, encrypted beaconing containing the compressed log files to known njRAT C2 infrastructure.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_NJLOGGER {
    meta:
        description = "Detects Njlogger (trojan)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "njlogger" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Njlogger Activity
id: 9f245f8471b1926416478d0494463a69
status: experimental
description: Detects generic indicators of the njlogger malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*njlogger*"
    condition: selection
level: medium

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Immediately isolate the infected endpoint from the network to prevent further exfiltration of the captured keystroke logs.
2. Assume all passwords typed on the infected machine (including Domain Admin credentials if applicable) are completely compromised and initiate an immediate, enterprise-wide password reset for that user.
3. Run a full memory analysis (RAM dump) to identify the running Njlogger process and extract any decryption keys for the local log files to determine exactly what data was stolen.
4. Investigate the network logs to identify the C2 server receiving the keystroke data and block it.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not allow the user to simply change their password *on the infected machine*; the keylogger will immediately capture the new password.
2. Avoid relying solely on basic file deletion to remediate; keyloggers are often injected into legitimate processes, requiring a reboot or advanced EDR remediation to fully clear the hook.

References & External Analysis

• Search "njlogger" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Scrop
• Fakesmoke
• Omaneat
• Remoxec
• Bancteian

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/njlogger.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.