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All About SMB

The first step of enumerating networks is to identify common network services. These are Telnet, SMB and FTP.

First step of enumeration is to conduct a port scan using nmap.

A good tool to use to enumerate networks is enum4linux.

What is SMB?

SMB - Server Message Block Protocol - is a client-server communication protocol used for sharing access to files, printers, serial ports and other resources on a network. [source]

Servers make file systems and other resources (printers, named pipes, APIs) available to clients on the network. Client computers may have their own hard disks, but they also want access to the shared file systems and printers on the servers.

The SMB protocol is known as a response-request protocol, meaning that it transmits multiple messages between the client and server to establish a connection. Clients connect to servers using TCP/IP (actually NetBIOS over TCP/IP as specified in RFC1001 and RFC1002), NetBEUI or IPX/SPX.

How does SMB work?






Once they have established a connection, clients can then send commands (SMBs) to the server that allow them to access shares, open files, read and write files, and generally do all the sort of things that you want to do with a file system. However, in the case of SMB, these things are done over the network.

What runs SMB?

Microsoft Windows operating systems since Windows 95 have included client and server SMB protocol support. Samba, an open source server that supports the SMB protocol, was released for Unix systems.

Enum4Linux

Enum4linux is a tool used to enumerate SMB shares on both Windows and Linux systems. It is basically a wrapper around the tools in the Samba package and makes it easy to quickly extract information from the target pertaining to SMB. It's installed by default on Parrot and Kali, however if you need to install it, you can do so from the official github.

The syntax of Enum4Linux is nice and simple: "enum4linux [options] ip"

TAG            FUNCTION

-U             get userlist
-M             get machine list
-N             get namelist dump (different from -U and-M)
-S             get sharelist
-P             get password policy information
-G             get group and member list

-a             all of the above (full basic enumeration)

 

Types of SMB Exploit

While there are vulnerabilities such as CVE-2017-7494 that can allow remote code execution by exploiting SMB, you're more likely to encounter a situation where the best way into a system is due to misconfigurations in the system. In this case, we're going to be exploiting anonymous SMB share access- a common misconfiguration that can allow us to gain information that will lead to a shell.

You can use enum4linux along with smbclient to get information.

Method Breakdown

So, from our enumeration stage, we know:

    - The SMB share location

    - The name of an interesting SMB share

SMBClient

Because we're trying to access an SMB share, we need a client to access resources on servers. We will be using SMBClient because it's part of the default samba suite. While it is available by default on Kali and Parrot, if you do need to install it, you can find the documentation here.

We can remotely access the SMB share using the syntax:

smbclient //[IP]/[SHARE]

Followed by the tags:

-U [name] : to specify the user

-p [port] : to specify the port

What would be the correct syntax to access an SMB share called "secret" as user "suit" on a machine with the IP 10.10.10.2 on the default port?

smbclient //10.10.10.2/secret -U suit -p 139 

Sometimes, smb will allow anonymous access. 

smbclient //10.10.229.72/profiles -U Anonymous

TIP: Use "smbget" to download files to your local machine.

 

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