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The **_Network Basic Input Output System_ (NetBIOS)** is a software protocol designed to enable applications, PCs, and Desktops within a local area network (LAN) to interact with network hardware and **facilitate the transmission of data across the network**. The identification and location of software applications operating on a NetBIOS network are achieved through their NetBIOS names, which can be up to 16 characters in length and are often distinct from the computer name. A NetBIOS session between two applications is initiated when one application (acting as the client) issues a command to "call" another application (acting as the server) utilizing **TCP Port 139**.
Technically, Port 139 is referred to as ‘NBT over IP’, whereas Port 445 is identified as ‘SMB over IP’. The acronym **SMB** stands for ‘**Server Message Blocks**’, which is also modernly known as the **Common Internet File System (CIFS)**. As an application-layer network protocol, SMB/CIFS is primarily utilized to enable shared access to files, printers, serial ports, and facilitate various forms of communication between nodes on a network.
For example, in the context of Windows, it is highlighted that SMB can operate directly over TCP/IP, eliminating the necessity for NetBIOS over TCP/IP, through the utilization of port 445. Conversely, on different systems, the employment of port 139 is observed, indicating that SMB is being executed in conjunction with NetBIOS over TCP/IP.
The **Server Message Block (SMB)** protocol, operating in a **client-server** model, is designed for regulating **access to files**, directories, and other network resources like printers and routers. Primarily utilized within the **Windows** operating system series, SMB ensures backward compatibility, allowing devices with newer versions of Microsoft's operating system to seamlessly interact with those running older versions. Additionally, the **Samba** project offers a free software solution, enabling SMB's implementation on **Linux** and Unix systems, thereby facilitating cross-platform communication through SMB.
Shares, representing **arbitrary parts of the local file system**, can be provided by an SMB server, making the hierarchy visible to a client partly **independent** from the server's actual structure. The **Access Control Lists (ACLs)**, which define **access rights**, allow for **fine-grained control** over user permissions, including attributes like **`execute`**, **`read`**, and **`full access`**. These permissions can be assigned to individual users or groups, based on the shares, and are distinct from the local permissions set on the server.
Access to the IPC$ share can be obtained through an anonymous null session, allowing for interaction with services exposed via named pipes. The utility `enum4linux` is useful for this purpose. Utilized properly, it enables the acquisition of:
This functionality is critical for network administrators and security professionals to assess the security posture of SMB (Server Message Block) services on a network. `enum4linux` provides a comprehensive view of the target system's SMB environment, which is essential for identifying potential vulnerabilities and ensuring that the SMB services are properly secured.
```bash
enum4linux -a target_ip
```
The above command is an example of how `enum4linux` might be used to perform a full enumeration against a target specified by `target_ip`.
If you don't know what is NTLM or you want to know how it works and how to abuse it, you will find very interesting this page about **NTLM** where is explained **how this protocol works and how you can take advantage of it:**
To look for possible exploits to the SMB version it important to know which version is being used. If this information does not appear in other used tools, you can:
It may be possible that you are restricted to display any shares of the host machine and when you try to list them it appears as if there aren't any shares to connect to. Thus it might be worth a short to try to manually connect to a share. To enumerate the shares manually you might want to look for responses like NT\_STATUS\_ACCESS\_DENIED and NT\_STATUS\_BAD\_NETWORK\_NAME, when using a valid session (e.g. null session or valid credentials). These may indicate whether the share exists and you do not have access to it or the share does not exist at all.
Specially interesting from shares are the files called **`Registry.xml`** as they **may contain passwords** for users configured with **autologon** via Group Policy. Or **`web.config`** files as they contains credentials.
{% hint style="info" %}
The **SYSVOL share** is **readable** by all authenticated users in the domain. In there you may **find** many different batch, VBScript, and PowerShell **scripts**.\
You should **check** the **scripts** inside of it as you might **find** sensitive info such as **passwords**.
crackmapexec can execute commands **abusing** any of **mmcexec, smbexec, atexec, wmiexec** being **wmiexec** the **default** method. You can indicate which option you prefer to use with the parameter `--exec-method`:
Both options will **create a new service** (using _\pipe\svcctl_ via SMB) in the victim machine and use it to **execute something** (**psexec** will **upload** an executable file to ADMIN$ share and **smbexec** will point to **cmd.exe/powershell.exe** and put in the arguments the payload --**file-less technique-**-).\
This attack uses the Responder toolkit to **capture SMB authentication sessions** on an internal network, and **relays** them to a **target machine**. If the authentication **session is successful**, it will automatically drop you into a **system****shell**.\
[**More information about this attack here.**](../generic-methodologies-and-resources/pentesting-network/spoofing-llmnr-nbt-ns-mdns-dns-and-wpad-and-relay-attacks.md)
The Windows library URLMon.dll automatically try to authenticaticate to the host when a page tries to access some contect via SMB, for example: `img src="\\10.10.10.10\path\image.jpg"`
Similar to SMB Trapping, planting malicious files onto a target system (via SMB, for example) can illicit an SMB authentication attempt, allowing the NetNTLMv2 hash to be intercepted with a tool such as Responder. The hash can then be cracked offline or used in an [SMB relay attack](pentesting-smb.md#smb-relay-attack).
While Port 139 is known technically as ‘NBT over IP’, Port 445 is ‘SMB over IP’. SMB stands for ‘Server Message Blocks’. Server Message Block in modern language is also known as Common Internet File System. The system operates as an application-layer network protocol primarily used for offering shared access to files, printers, serial ports, and other sorts of communications between nodes on a network.
#These are the commands I run in order every time I see an open SMB port
<summary><strong>Learn AWS hacking from zero to hero with</strong><ahref="https://training.hacktricks.xyz/courses/arte"><strong>htARTE (HackTricks AWS Red Team Expert)</strong></a><strong>!</strong></summary>
* If you want to see your **company advertised in HackTricks** or **download HackTricks in PDF** Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** 🐦 [**@carlospolopm**](https://twitter.com/carlospolopm)**.**
* **Share your hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.