Smbd

Overview

Worm:Win32/Smbd (or similar heuristic detections for SMB-exploiting worms) refers to a class of self-propagating malware that heavily relies on the Server Message Block (SMB) protocol for lateral movement across local area networks (LANs). These worms exploit vulnerabilities in Windows SMB implementations (historically MS08-067 or MS17-010/EternalBlue) or utilize brute-force credential stuffing against administrative shares to spread rapidly without user interaction.

Understanding SMB Network Worms
To an end-user, an infection might cause severe network slowdowns or sudden system reboots (often associated with successful SMB exploits). For a network administrator, an SMB worm represents a catastrophic outbreak scenario. A single infected laptop brought into the office can compromise the entire corporate network within minutes by scanning and exploiting vulnerable servers and workstations on the same subnet.

Execution and Lateral Movement Mechanics
Once an initial host is compromised (often via phishing or an external exploit), the Smbd worm begins its propagation phase. It actively scans the local subnet (`T1046`) on ports 139 and 445 (SMB) for other Windows machines. When it finds a target, it attempts to gain access. It may use hardcoded, highly privileged exploits (like EternalBlue) (`T1210`) to execute arbitrary code directly in the kernel of the remote machine. Alternatively, it may use stolen credentials or brute-force dictionaries to authenticate to the `ADMIN$` or `C$` hidden network shares (`T1021.002`). Upon successful connection, it copies its own executable to the remote machine (`T1570`) and uses tools like PsExec or WMI (`T1047`) to execute the copied payload, perpetuating the cycle.

Indicators of Compromise & Impact
The impact is total network compromise and massive internal bandwidth consumption. Host-based IoCs include EDR alerts for unexpected inbound connections on port 445 resulting in the creation of `.exe` files in `C:\Windows\` or `C:\Windows\System32\`, followed by immediate execution. Network IoCs include massive spikes in horizontal (east-west) SMB traffic on ports 139/445, as infected machines aggressively scan their neighbors.

MITRE ATT&CK Techniques

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

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

Sigma Rule

title: Suspicious Smbd Activity
id: 28afc24826e573a4a7cca1ce1856833d
status: experimental
description: Detects generic indicators of the smbd malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*smbd*"
    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 network at the switch/VLAN level to contain the horizontal spread of the worm.
2. Enforce strict firewall rules blocking all workstation-to-workstation (east-west) SMB traffic (ports 139 and 445); workstations rarely need to share files directly with each other.
3. Identify the vulnerable systems (missing critical Microsoft SMB patches) and immediately deploy the necessary updates.
4. If credentials were used for propagation, force an immediate reset of all Domain Admin and local administrator passwords.

What to Avoid

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

1. Do not allow unpatched, legacy operating systems (like Windows XP or Server 2003) to reside on the same network segments as critical infrastructure.
2. Avoid leaving default local administrator accounts active with the same password across the enterprise, as worms exploit this for easy lateral movement.

References & External Analysis

• Search "smbd" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Installtoolbar
• Invader
• Hakopsbot
• Zylom
• Alnaddy

Machine-readable

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