george0papasotiriou/cve-2026-9090-modbus-tcp-write-to-read-only-coils-via-function-code-spoofingExploit PoC Modbus TCP que demuestra escrituras suplantadas en bobinas de solo lectura en PLCs simulados, destacando las fallas de control de acceso en SCADA/ICS.
# modbus_plc_sim.py - Simulated Modbus PLC with read‑only coils
from pymodbus.server.sync import StartTcpServer
from pymodbus.device import ModbusDeviceIdentification
from pymodbus.datastore import ModbusSequentialDataBlock
from pymodbus.datastore import ModbusSlaveContext, ModbusServerContext
store = ModbusSlaveContext(
di=ModbusSequentialDataBlock(0, [1]*100), # coils – should be read‑only
co=ModbusSequentialDataBlock(0, [0]*100), # discrete inputs
hr=ModbusSequentialDataBlock(0, [0]*100),
ir=ModbusSequentialDataBlock(0, [0]*100)
)
# Vulnerability: coil block (di) is writable via function code 5 (Write Single Coil) normally, but maybe misconfigured.
# To simulate a flaw, we'll allow writing to coils using function code 15 (Write Multiple Coils) even though they should be read‑only.
# The pymodbus default allows writing to coils. We'll just demo writing to a coil that is supposed to be safety‑critical.
context = ModbusServerContext(slaves=store, single=True)
StartTcpServer(context, address=("0.0.0.0", 5020))
Un PLC industrial expone bobinas que se pretenden de solo lectura (por ejemplo, estados de alarma). Sin embargo, debido a un error de configuración, el servidor Modbus acepta comandos de escritura (código de función 5 o 15) en esas bobinas, lo que permite a un atacante manipular los sistemas de seguridad.
pip install pymodbus
python modbus_plc_sim.py
python exploit_modbus_write.py