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AUSCERT External Security Bulletin Redistribution
Advisory (ICSA-19-106-03) PLC Cycle Time Influences
17 April 2019
AusCERT Security Bulletin Summary
Product: ABB 1SAP120600R0071 PM554-TP-ETH PLC
Schneider Modicon M221 PLC
Siemens 6ES7211-1AE40-0XB0 Simatic S7-1211
Siemens 6ES7314-6EH04-0AB0 Simatic S7-314
Siemens 6ED1052-1CC01-0BA8 Logo! 8
WAGO 750-889 Controller KNX IP
WAGO 750-831 Controller BACnet/IP
WAGO 750-880 Controller ETH
WAGO 750-8100 Controller PFC100
Operating System: Network Appliance
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2019-10953
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PLC Cycle Time Influences
Original release date: April 16, 2019
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1. EXECUTIVE SUMMARY
o CVSS v3 7.5
o ATTENTION: Exploitable remotely/low skill level to exploit/public exploits
o Vendors: ABB, Phoenix Contact, Schneider Electric, Siemens, WAGO
o Equipment: Programmable Logic Controllers
o Vulnerability: Uncontrolled Resource Consumption
2. RISK EVALUATION
High network load can consume CPU power in such a way that the normal operation
of the device can be affected;that is, the configured cycle time can be
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
The following programmable logic controllers (PLCs) are affected:
o ABB 1SAP120600R0071 PM554-TP-ETH
3.1.2 PHOENIX CONTACT
o Phoenix Contact 2700974 ILC 151 ETH
3.1.3 SCHNEIDER ELECTRIC
o Schneider Modicon M221
o Siemens 6ES7211-1AE40-0XB0 Simatic S7-1211
o Siemens 6ES7314-6EH04-0AB0 Simatic S7-314
o Siemens 6ED1052-1CC01-0BA8 Logo! 8
o WAGO 750-889 Controller KNX IP
o WAGO 750-8100 Controller PFC100
o WAGO 750-880 Controller ETH
o WAGO 750-831 Controller BACnet/IP
3.2 VULNERABILITY OVERVIEW
3.2.1 UNCONTROLLED RESOURCE CONSUMPTION CWE-400
Researchers have found some controllers are susceptible to a denial-of-service
attack due to a flood of network packets.
CVE-2019-10953 has been assigned to this vulnerability. A CVSS v3 base score of
7.5 has been calculated; the CVSS vector string is ( AV:N/AC:L/PR:N/UI:N/S:U/
ABB, Phoenix, Schneider Electric, Siemens, and WAGO are companies based in
Europe that deploy their PLCs worldwide across the following critical
infrastructure sectors: Chemical, Commercial Facilities, Critical
Manufacturing, Dams, Energy, Food and Agriculture, Transportation Systems, and
Water and Wastewater Systems.
Matthias Niedermaier (Hochschule Augsburg), Jan-Ole Malchow (Freie Universitat
Berlin), and Florian Fischer (Hochschule Augsburg) reported this vulnerability
PLC vendors have responded to queries about this report with the following
ABB concludes the reported behavior is not a vulnerability but is due to a
misconfiguration of the PLC watchdog, which was left in the default factory
settings. This has led to a configuration that does not match the expectations
expressed in the test cases and the result is the PLC not reacting as intended.
This misconfiguration can be fixed by setting an appropriate combination of
task priority, task cycle time, and watchdog settings. Please see the "Onboard
Ethernet Handling in CPU Firmware" chapter (System Technology for AC500 V2
Products > System Technology of CPU and Overall System > Onboard Technologies >
Ethernet > Ethernet Protocols and Ports for AC500 V2 Products > Onboard
Ethernet Handling in CPU Firmware) for further guidance.
4.2 PHOENIX CONTACT
Phoenix Contact acknowledges this as a "known, won't fix" issue for old
products. Currently available products provide countermeasures to mitigate the
impact on the safety-related functionality. Phoenix Contact urges users to
adhere to the application note available at:
4.3 SCHNEIDER ELECTRIC
Fixes are available in the Modicon M221 firmware v184.108.40.206 and the EcoStruxure
Machine Expert - Basic v1.0 software (formerly SoMachine Basic) using either of
the following options:
Use the following link:
Or run the Schneider Electric Software Update tool in order to download and
install EcoStruxure Machine Expert - Basic v1.0 software.
Schneider Electric's security notice SEVD-2019-045-01 is available at the
Schneider Electric strongly recommends following industry cybersecurity best
practices, such as:
o Physical controls should be in place so no unauthorized person would have
access to the ICS and safety controllers, peripheral equipment, or the ICS
and safety networks.
o All controllers should reside in locked cabinets and never be left in the
o All programming software should be kept in locked cabinets and should never
be connected to any network other than the network for the devices it is
o All methods of mobile data exchange with the isolated network (e.g., CDs,
USB drives, etc.)should be scanned before use in terminals or any node
connected to these networks.
o Laptops that have connected to any other network besides the intended
network should never be allowed to connect to the safety or control
networks without proper sanitation.
Siemens has investigated the vulnerability report on PLC cycle time influences
and concludes the report does not demonstrate a valid vulnerability for Siemens
WAGO recommends users operate the devices in closed networks or protect them
with a firewall against unauthorized access. Another recommended mitigation is
to limit network traffic via the switch rate limit feature according to
Please also consult the product manuals on the WAGO website, as this is a known
problem for some devices. Links to product manuals and specific instructions
about how to limit switch rates can be found in the VDE CERT advisory:
NCCIC recommends users take defensive measures to minimize the risk of
exploitation of this vulnerability. Specifically, users should:
o Minimize network exposure for all control system devices and/or systems,
and ensure that they are not accessible from the Internet .
o Locate control system networks and remote devices behind firewalls, and
isolate them from the business network.
o When remote access is required, use secure methods, such as Virtual Private
Networks (VPNs), recognizing that VPNs may have vulnerabilities and should
be updated to the most current version available. Also recognize that VPN
is only as secure as the connected devices.
NCCIC reminds organizations to perform proper impact analysis and risk
assessment prior to deploying defensive measures.
NCCIC also provides a section for control systems security recommended
practices on the ICS-CERT web page. Several recommended practices are available
for reading and download, including Improving Industrial Control Systems
Cybersecurity with Defense-in-Depth Strategies .
Additional mitigation guidance and recommended practices are publicly available
on the ICS-CERT website in the Technical Information Paper,
ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation
Organizations observing any suspected malicious activity should follow their
established internal procedures and report their findings to NCCIC for tracking
and correlation against other incidents.
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