Feebs

Overview

Executive Summary

Propagation and Execution Lifecycle

• Mass-Mailing (Worm Capability): Upon execution, Feebs harvests email addresses from the victim's local files (address books, cached web pages, document files). It then utilizes its own built-in SMTP engine to spam copies of itself to those addresses, spoofing the "From" address to increase the likelihood the recipient will open the malicious attachment (often a ZIP file containing a disguised executable or `.scr` file).
• Polymorphism: Every time Feebs sends a copy of itself, it alters its internal code structure and encrypts its payload differently. This ensures that the file hash is completely unique for every single victim, rendering static AV signatures useless.
• System Sabotage: Once active, Feebs attempts to disable local antivirus and firewall software, modifies the Windows `HOSTS` file to block access to security vendor websites, and drops secondary trojans or backdoors to allow the attacker persistent access.

Threat Assessment

Eradication and Incident Response

• Aggressive Network Isolation: Infected machines must be immediately disconnected from the LAN to halt the outbound spam traffic and prevent lateral spread via network shares.
• Mail Gateway Filtering: Implement aggressive filtering at the Secure Email Gateway (SEG) to block inbound and outbound executable attachments, even within ZIP archives.
• Behavioral EDR: Because Feebs is highly polymorphic, defenses must rely on heuristic and behavioral EDR tools that detect its anomalous actions (e.g., an unknown process attempting to establish SMTP connections or modifying the `HOSTS` file).

Known aliases

Threat reports may refer to this family under multiple names:

• Worm.Win32.Feebs
• W32/Feebs
• Trojan.Feebs

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:

• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

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:

rule MALWARE_WIN_FEEBS_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Feebs"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "feebs" ascii wide nocase
        $s2 = "worm.win32.feebs" ascii wide nocase
        $s3 = "w32/feebs" ascii wide nocase
        $s4 = "trojan.feebs" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Feebs (Trojan) Execution & Triage
id: 576985cc-81a7-5ec3-8873-078c1c5b8046
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Feebs 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/feebs
- 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.t1566_001
- attack.t1562_001
- attack.t1562_004
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: medium

rule MALWARE_WIN_FEEBS_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Feebs 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 = "feebs" 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.

1. Sever network connectivity for the flagged endpoint to terminate persistent command-and-control (C2) communication channels and stop Feebs from retrieving secondary stage payloads.
2. Capture process memory triage to detect and terminate malicious threads injected by Feebs into legitimate system processes such as explorer.exe or svchost.exe.
3. Audit Windows Registry Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) and Task Scheduler entries to locate and purge Feebs persistence hooks.
4. Deploy updated enterprise EDR detection signatures and conduct an out-of-band endpoint scan to isolate dropped binaries and staged payloads.
5. Rotate all credentials, domain user passwords, and session cookies active on the system during the Feebs execution timeframe.

What to Avoid

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

1. Do not assume the incident is resolved simply because an antivirus tool removed the initial Feebs dropper; always verify that secondary payloads and persistence hooks have been eradicated.
2. Avoid logging in with Domain Admin or privileged credentials on a machine suspected of running Feebs until memory triage is complete.
3. Do not delay host isolation; automated lateral movement and credential dumping can occur within minutes of initial execution.

References & External Analysis

• Search "feebs" on VirusTotal (External Analysis)
• Search "feebs" on Any.Run (Sandbox Sandbox)
• Search "feebs" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Genericrxbg
• Indigorose
• 2345Cn
• Havex
• Habbo
• Yahoopass
• Messiah
• Ponmocup

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/feebs.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.