3Proxy

Overview

HackTool:Win32/3proxy (or simply **3proxy**) is a highly versatile, open-source proxy server. While it is a legitimate administrative tool designed to route network traffic, it is heavily abused by threat actors (acting as a 'Dual-Use Tool' or 'Living off the Land Binary' - LoLBin). Attackers install 3proxy on compromised endpoints (especially home routers, IoT devices, and Windows servers) to silently route their malicious traffic through the victim's IP address, masking their true location.

Understanding 3proxy Abuse
To an infected user, the presence of 3proxy is entirely invisible; it runs silently in the background. For a threat intelligence analyst, the unauthorized presence of 3proxy indicates that the endpoint has been conscripted into an illegal proxy botnet (like the RSOCKS botnet). Cybercriminals rent access to these proxy networks to conduct credential stuffing attacks, click fraud, or to access geo-blocked banking portals without triggering fraud alerts (since the traffic appears to come from a residential IP).

Execution and Proxy Network Mechanics
Attackers typically gain access via brute-forcing weak SSH/RDP credentials (`T1110.001`) or exploiting unpatched vulnerabilities (`T1190`). Once they have a foothold, they download the pre-compiled 3proxy executable (`T1105`). They configure it (often via a simple `.cfg` file) to run quietly on a high, non-standard port and establish persistence via a Scheduled Task or systemd service (`T1543`). The attacker's C2 server then registers the victim's IP address as an active proxy node. When a cybercriminal buys proxy access, their traffic is routed through the attacker's server, into the victim's 3proxy instance (`T1090`), and then out to the target website.

Indicators of Compromise & Impact
The impact is that the victim's IP address is used for illegal activity, potentially leading to their IP being blacklisted by major services (Netflix, banks). Incident responders should investigate EDR alerts for the execution of `3proxy.exe` from unexpected directories (like `%Temp%`). Network logs will show a high volume of inbound connections to a non-standard port, followed immediately by outbound connections to various internet targets, indicative of proxy routing.

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:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

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_3PROXY {
    meta:
        description = "Detects 3Proxy (advanced_threat)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "3proxy" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious 3Proxy Activity
id: 1c0bbf0b4844b0096042f765aaaaeb08
status: experimental
description: Detects generic indicators of the 3proxy malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*3proxy*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Isolate the endpoint to immediately sever the proxy connections being routed through the machine.
2. Identify and terminate the running `3proxy` process, and delete the associated executable and `.cfg` configuration file.
3. Audit Scheduled Tasks, Registry Run keys, and Services to remove the persistence mechanism that launches the proxy.
4. Investigate how the attacker gained initial access (e.g., exposed RDP, weak passwords) and remediate the vulnerability to prevent reinfection.

What to Avoid

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

1. Do not assume 3proxy is inherently malware; check with system administrators to ensure it wasn't installed legitimately for network routing (though rare on standard endpoints).
2. Avoid relying solely on file deletion, as the attacker may still have the initial access backdoor (like a web shell or compromised credentials) used to install it.

References & External Analysis

• Search "3proxy" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Openinstall
• Chindo
• Spammy
• Lynx
• Superspy

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/3proxy.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.