ESB-2019.0446 - [Appliance] Siemens SIMATIC S7-300 CPU: Denial of service - Remote/unauthenticated 2019-02-13

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             AUSCERT External Security Bulletin Redistribution

                               ESB-2019.0446
           Advisory (ICSA-19-043-04) Siemens SIMATIC S7-300 CPU
                             13 February 2019

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Siemens SIMATIC S7-300 CPU
Publisher:         ICS-CERT
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-16561  

Original Bulletin: 
   https://ics-cert.us-cert.gov/advisories/ICSA-19-043-04

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Advisory (ICSA-19-043-04)

Siemens SIMATIC S7-300 CPU

Original release date: February 12, 2019

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1. EXECUTIVE SUMMARY

  o CVSS v3 7.5
  o ATTENTION : Exploitable remotely/low skill level to exploit
  o Vendor : Siemens
  o Equipment : SIMATIC S7-300 CPU
  o Vulnerability : Improper Input Validation

2. RISK EVALUATION

Successful exploitation of this vulnerability could crash the device being
accessed, resulting in a denial-of-service condition.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

Siemens reports the following SIMATIC S7-300 CPU product is affected:

  o SIMATIC S7-300 CPUs: All versions prior to v3.X.16

3.2 VULNERABILITY OVERVIEW

3.2.1 IMPROPER INPUT VALIDATION CWE-20

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 send a specially crafted S7
communication packet to a communication interface of the CPU. This includes
Ethernet, PROFIBUS, and Multi Point Interfaces (MPI). The vulnerability could
allow a denial-of-service condition of the core functionality of the CPU.

CVE-2018-16561 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/I:N/A:H ).

3.3 BACKGROUND

  o CRITICAL INFRASTRUCTURE SECTORS : Chemical, Critical Manufacturing, Energy,
    Food and Agriculture, Water and Wastewater Systems
  o COUNTRIES/AREAS DEPLOYED : Worldwide
  o COMPANY HEADQUARTERS LOCATION : Germany

3.4 RESEARCHER

China Industrial Control Systems Cyber Emergency Response Team (CIC) reported
this vulnerability to Siemens.

4. MITIGATIONS

Siemens recommends users update to Version 3.X.16, which can be downloaded from
the following link:

https://support.industry.siemens.com/cs/ww/en/ps/13752/dl

Siemens has identified the following specific workarounds and mitigations users
can apply to reduce the risk:

  o Siemens recommends operating the devices only within trusted networks

As a general security measure, Siemens strongly recommends protecting network
access to devices with appropriate mechanisms. In order to operate the devices
in a protected IT environment, Siemens recommends configuring the environment
according to Siemens' operational guidelines for industrial security ( https://
www.siemens.com/cert/operational-guidelines-industrial-security ), and
following the recommendations in the product manuals.

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

https://www.siemens.com/industrialsecurity

For more information on this vulnerability and associated software updates,
please see Siemens security advisory SSA-306710 on their website:

https://www.siemens.com/cert/advisories

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
Strategies .

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.

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