Protocol Deep Dive

SMB Protocol Guide

Comprehensive technical guide to the Server Message Block (SMB) protocol, its evolution, architecture, and security implications for penetration testing.

Protocol Overview

Basic Information

Full Name:Server Message Block (SMB)
Developer:Microsoft Corporation
First Release:1983
Current Version:SMB 3.1.1

Purpose & Usage

Network file sharing protocol

Also Known As:

CIFS - Common Internet File System
Microsoft-DS
Protocol Stats
6
Major Versions
41
Years of Evolution
2
Primary Ports
SMB Protocol Versions
Evolution of the SMB protocol from 1983 to present day

SMB 1.0

1983
Deprecated - should be disabled

Key Features

  • Basic file sharing
  • Print sharing
  • Named pipes

Security

Weak authentication, numerous vulnerabilities

Ports:
139
445

Recommendation

❌ Disable immediately

SMB 2.0

2006
Legacy but still supported

Key Features

  • Improved performance
  • Larger buffer sizes
  • Symbolic links

Security

Enhanced security, message signing

Ports:
445

Recommendation

⚠️ Upgrade when possible

SMB 2.1

2008
Legacy but still supported

Key Features

  • Opportunistic locking improvements
  • Large MTU support

Security

Improved authentication mechanisms

Ports:
445

Recommendation

⚠️ Upgrade when possible

SMB 3.0

2012
Modern and secure

Key Features

  • End-to-end encryption
  • Scale-out file servers
  • SMB Direct over RDMA

Security

AES encryption, secure dialects

Ports:
445

Recommendation

✅ Safe to use

SMB 3.0.2

2013
Modern and secure

Key Features

  • Performance improvements
  • Better error handling

Security

Enhanced encryption algorithms

Ports:
445

Recommendation

✅ Safe to use

SMB 3.1.1

2015
Current recommended version

Key Features

  • Pre-authentication integrity
  • AES-128-GCM encryption
  • Directory leasing

Security

Strongest security implementation

Ports:
445

Recommendation

✅ Safe to use

Protocol Architecture
Understanding SMB protocol layers and components

Protocol Stack

Application Layer

User applications accessing shared resources

SMB/CIFS Client

SMB Protocol Layer

SMB protocol implementation

SMB 1.0/2.0/3.0

Transport Layer

Network transport mechanisms

TCP
NetBIOS over TCP
Named Pipes

Network Layer

Network communication

IP
NetBEUI
IPX/SPX

Key Components

SMB Client

Initiates requests to SMB servers

Examples:
Windows Explorer
smbclient
mount.cifs

SMB Server

Provides shared resources and services

Examples:
Windows File Server
Samba
NAS devices

SMB Redirector

Routes SMB requests over network

Examples:
Windows Workstation service
Client for Microsoft Networks
Security Architecture
Authentication methods and encryption mechanisms in SMB

Authentication Methods

NTLM

Medium

NT LAN Manager authentication

NTLMv1 vulnerable, NTLMv2 better but still weak

NTLMv1
NTLMv2

Kerberos

Secure

Ticket-based authentication

Strong authentication when properly implemented

Kerberos v5

Anonymous

Vulnerable

No authentication required

Highly insecure, should be disabled

Null sessions

Encryption & Integrity

SMB 1.0

Encryption: None by default
Integrity: Weak or none
Vulnerabilities:
  • Plaintext passwords
  • Man-in-the-middle attacks

SMB 2.0/2.1

Encryption: Optional message signing
Integrity: Message signing available
Vulnerabilities:
  • Signing can be disabled
  • Downgrade attacks

SMB 3.0+

Encryption: AES-128-CCM, AES-128-GCM
Integrity: Built-in integrity checking
Vulnerabilities:
  • Configuration dependent
  • Implementation flaws
Common Vulnerabilities
Typical security weaknesses found in SMB implementations

Protocol Vulnerabilities

  • SMBv1 inherent security weaknesses
  • Null session enumeration
  • Message signing bypass
  • Downgrade attacks to weaker protocols

Authentication Weaknesses

  • NTLM relay attacks
  • Pass-the-hash attacks
  • Credential stuffing
  • Weak password policies

Implementation Flaws

  • Buffer overflow vulnerabilities
  • Remote code execution flaws
  • Memory corruption issues
  • Input validation failures

Configuration Issues

  • Unnecessary shares exposed
  • Weak access controls
  • Default credentials
  • Unencrypted communications