Ircfast

Overview

Worm/Trojan:Win32/Ircfast is a network worm and botnet agent that leverages the Internet Relay Chat (IRC) protocol for command and control. Prevalent during the peak era of IRC-based botnets, Ircfast is designed to compromise a system, self-propagate across network shares, and connect the infected host to an attacker-controlled chat channel to receive commands, typically for participating in Distributed Denial of Service (DDoS) attacks.

Understanding Ircfast (IRC Botnets)
To an end-user, an Ircfast infection might cause general system sluggishness and network latency. For a security team, it represents a noisy, highly disruptive infection. Unlike modern botnets that use Tor or encrypted HTTPS, IRC botnets are 'loud' (`T1071.001`), transmitting commands in cleartext over well-known ports, making them easier to detect but very difficult to eradicate once they gain a foothold in a flat network.

Execution and Propagation Mechanics
Ircfast spreads primarily by scanning the local subnet for open Windows administrative shares (IPC$, C$, ADMIN$) and attempting brute-force password guessing (`T1110.001`). Once it successfully copies itself (`T1105`) and executes on a new machine, it establishes persistence via the Registry Run keys. The malware then initiates a connection to a hardcoded IRC server (often on port 6667), joins a specific hidden channel, and waits for commands from the botmaster. These commands can instruct the bot to download additional malware, execute a UDP/TCP flood attack (`T1498`), or aggressively scan for new targets (`T1046`).

Indicators of Compromise & Impact
The primary impact is network congestion, participation in illegal DDoS activities, and potential data theft. Network IoCs are highly prominent: persistent outbound TCP connections to external IP addresses on port 6667 (or alternative IRC ports like 6660-6669), and massive spikes in outbound scanning traffic (TCP 135/445) as the worm attempts to spread. Host IoCs include unknown executables running from the Windows System32 directory and corresponding Registry persistence entries.

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:

• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.

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

Sigma Rule

title: Suspicious Ircfast Activity
id: 5446af188a6e1def4b1024f426be2f3e
status: experimental
description: Detects generic indicators of the ircfast malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*ircfast*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Immediately segment the infected VLANs to prevent the worm from traversing the entire enterprise network.
2. Block outbound IRC traffic (TCP port 6667 and related ports) at the perimeter firewall to sever the command and control link.
3. Enforce strong password policies across all service accounts and local administrator accounts to defeat the worm's brute-forcing mechanism.
4. Use enterprise EDR to hunt for the specific Ircfast executables and Registry Run keys across all endpoints simultaneously.

What to Avoid

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

1. Do not attempt to clean individual machines without first isolating the network, as the worm will immediately re-infect them via administrative shares.
2. Avoid ignoring outbound traffic to unfamiliar ports, as IRC botnets frequently shift their C2 to non-standard high ports to evade simple firewall rules.

References & External Analysis

• Search "ircfast" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Confuser
• Wfpdisabler
• Suixin
• Wintrim
• Infinitetear

Machine-readable

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