Ircfast
Table of Contents
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 our technical analysis hubs and the official 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.
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-PSA | Port Scan Analysis | Detect | T1046 | Deploy network intrusion detection (NIDS) to identify sequential TCP SYN scans and unauthorized subnet reconnaissance. |
D3-WAF | Web Content Filtering & Inspection | Filter | T1071.001 | Block newly registered domains (NRDs) and inspect HTTP Host and URI headers for known C2 profiles. |
D3-AL | Account Lockout Policy | Harden | T1110.001 | Enforce progressive delay and lockout thresholds on failed authentication attempts to thwart brute-force password guessing. |
D3-TR | Traffic Rate Limiting | Isolate | T1498 | Deploy BGP Flowspec and edge scrubbing proxies to automatically throttle volumetric SYN and UDP reflection attacks. |
Tiered Detection Rules (Cisco CAIRN Model)
Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_IRCFAST_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Ircfast"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "ircfast" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Ircfast (Trojan) Execution & Triage
id: bbeb901a-dd29-5628-b335-5f34c6cce0bf
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Ircfast malware family. Detects suspicious execution from temporary user
directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/ircfast
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.trojan
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1046
- attack.t1071_001
- attack.t1498
- attack.t1110_001
logsource:
category: process_creation
product: windows
detection:
selection_process:
Image|endswith:
- \cmd.exe
- \powershell.exe
- \cscript.exe
- \wscript.exe
CommandLine|contains:
- AppData\Local\Temp
- -WindowStyle Hidden
- /e:jscript
- bitsadmin /transfer
condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_IRCFAST_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Ircfast tradecraft"
tier = "T3 - Attribution Fingerprint"
confidence = "High (Confirmed Family Signature)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
// Core family identifier & heuristic payload signatures
$attrib_str = "ircfast" ascii wide nocase
$pe_magic = "MZ" ascii
$net_marker = "http" ascii nocase
condition:
uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}Containment & Response Steps
Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.
- Immediately segment the infected VLANs to prevent the worm from traversing the entire enterprise network.
- Block outbound IRC traffic (TCP port 6667 and related ports) at the perimeter firewall to sever the command and control link.
- Enforce strong password policies across all service accounts and local administrator accounts to defeat the worm's brute-forcing mechanism.
- 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.
- Do not attempt to clean individual machines without first isolating the network, as the worm will immediately re-infect them via administrative shares.
- 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)
- Search "ircfast" on Any.Run (Sandbox Sandbox)
- Search "ircfast" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Ircfast and what threat category does it belong to?
Ircfast is classified as a Trojan. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments.
How does Ircfast establish persistence and evade defensive controls?
Ircfast typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks.
What are the essential incident response steps for mitigating a Ircfast compromise?
Security teams responding to Ircfast should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups.
What secondary payloads and staging behaviors are commonly associated with Ircfast?
Ircfast frequently operates as a loader or dropper designed to establish a foothold before downloading and executing secondary high-impact malware payloads. Depending on the threat actor's objectives, these dropped modules can range from ransomware and banking injects to modular infostealers and remote management backdoors.
How can security operations teams effectively detect and hunt for Ircfast across enterprise endpoints?
Defenders should hunt for Ircfast by deploying behavioral endpoint detection and response (EDR) rules that monitor suspicious process spawning (such as cmd.exe or powershell.exe spawned from office documents or temporary directories), anomalous outbound network connections from non-browser binaries, and unauthorized modifications to Windows Run keys and scheduled task registries.
How do I remove the Ircfast Trojan from Windows?
Manual removal of Ircfast is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
Is Ircfast a virus or a Trojan?
Ircfast is classified as a Trojan. Unlike traditional viruses that infect files, modern malware like Ircfast typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Ircfast infection?
Symptoms of Ircfast can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Trojans
Want to prevent Ircfast and similar threats from compromising your organization? Read our comprehensive defensive guide: Banking Trojan Protection for Businesses.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/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.