ESB-2018.1534 - [Appliance] Siemens SIMATIC S7-400 CPU: Denial of service - Remote/unauthenticated 2018-05-18

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             AUSCERT External Security Bulletin Redistribution

                        Siemens SIMATIC S7-400 CPU
                                18 May 2018


        AusCERT Security Bulletin Summary

Product:           Siemens SIMATIC S7-400 CPU
Publisher:         ICS-CERT
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-4850  

Original Bulletin:

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Advisory (ICSA-18-137-03)

Siemens SIMATIC S7-400 CPU

Original release date: May 17, 2018

Legal Notice

All information products included in are
provided "as is" for informational purposes only. The Department of Homeland
Security (DHS) does not provide any warranties of any kind regarding any
information contained within. DHS does not endorse any commercial product or
service, referenced in this product or otherwise. Further dissemination of this
product is governed by the Traffic Light Protocol (TLP) marking in the header.
For more information about TLP, see

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  * CVSS v3 7.5
  * ATTENTION: Exploitable remotely/low skill level to exploit
  * Vendor: Siemens
  * Equipment: SINAMIC S7-400 CPU
  * Vulnerability: Improper Input Validation


Successful exploitation of this vulnerability could cause a denial-of-service
condition of the CPU. The CPU will remain in DEFECT mode until a manual restart
is performed.



The following versions of SIMATIC S7-400, a CPU used for process controls, are

  * SIMATIC S7-400 (incl. F) CPU all hardware versions prior to, including,
    hardware V4.0,
  * SIMATIC S7-400 (incl. F) CPU hardware V5.0 with firmware versions prior to
    V5.2, and
  * SIMATIC S7-400H CPU all hardware versions prior to V4.5



The affected CPUs improperly validate S7 communication packets, which could
cause a denial-of-service condition of the CPU. The CPU will remain in DEFECT
mode until manual restart.

Successful exploitation requires an attacker to be able to send a specially
crafted S7 communication packet to a communication interface of the CPU. This
includes Ethernet, PROFIBUS, and multi-point interfaces (MPI). No user
interaction or privileges are required to exploit the security vulnerability.
This vulnerability could allow causing a denial-of-service condition of the
core functionality of the CPU, compromising the availability of the system.

CVE-2018-4850 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/C:N


  * Critical Infrastructure Sectors: Chemical, Critical Manufacturing, Energy,
    Food and Agriculture, Water and Wastewater Systems
  * Countries/Areas Deployed: Worldwide
  * Company Headquarters Location: Germany


Siemens ProductCERT reported this vulnerability to NCCIC.


Siemens has released updates for several affected products and recommends users
update to the new version.

  * SIMATIC S7-400 (incl. F) CPU all hardware versions prior to, and including,
    hardware V4.0: Upgrade to hardware V5.0 or newer.

  * SIMATIC S7-400 (incl. F) CPU hardware V5.0 with firmware versions prior to
    V5.2: Update to firmware V5.2 or newer.

  * SIMATIC S7-400H CPU all hardware versions prior to V4.5: Upgrade to
    hardware V6.0 or newer.

As a general security measure, Siemens strongly recommends protecting network
access to devices with appropriate mechanisms. In order to run the devices in a
protected IT environment, Siemens specifically recommends users configure the
environment according to Siemens? Operational Guidelines for Industrial
Security and follow the recommendations in the product manuals.

Additional information on industrial security by Siemens can be found at:

For more information on this vulnerability and associated software updates,
please see Siemens security advisory SSA-914382 on their website:

NCCIC recommends users take defensive measures to minimize the risk of
exploitation of this vulnerability. Specifically, users should:

  * Minimize network exposure for all control system devices and/or systems,
    and ensure that they are not accessible from the Internet.
  * Locate control system networks and remote devices behind firewalls, and
    isolate them from the business network.
  * 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.

No known public exploits specifically target this vulnerability.

Contact Information

For any questions related to this report, please contact the NCCIC at:

Toll Free: 1-888-282-0870

For industrial control systems cybersecurity information:  http:// 
or incident reporting:

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