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             AUSCERT External Security Bulletin Redistribution

        Siemens SIMATIC S7-300 CPU Denial-of-Service Vulnerability
                               6 March 2015


        AusCERT Security Bulletin Summary

Product:           Siemens SIMATIC S7-300 CPU Family
Publisher:         US-CERT
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2015-2177  

Original Bulletin: 

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Advisory (ICSA-15-064-04)

Siemens SIMATIC S7-300 CPU Denial-of-Service Vulnerability

Original release date: March 05, 2015

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Johannes Klick, Christian Pfahl, Martin Gebert, and Lucas Jacob from Freie 
Universitt Berlins work team SCADACS have identified a Denial-of-Service (DoS)
vulnerability in Siemens SIMATIC S7-300 CPUs. Siemens has developed 
mitigations for this vulnerability.

This vulnerability could be exploited remotely.


The following SIMATIC S7-300 CPUs are affected:

SIMATIC S7-300 CPU family: all versions.


This vulnerability could allow attackers to perform a DoS attack over the 
network without prior authentication against S7-300 CPUs under certain 
conditions. A cold restart is required to recover the system.

Impact to individual organizations depends on many factors that are unique to
each organization. NCCIC/ICS-CERT recommends that organizations evaluate the 
impact of this vulnerability based on their operational environment, 
architecture, and product implementation.


Siemens is a multinational company headquartered in Munich, Germany.

The affected product, SIMATIC S7-300 CPU, have been designed for process 
control in industrial environments. This product is deployed across several 
sectors including Chemical, Energy, Food and Agriculture, and Water and 
Wastewater Systems. Siemens estimates that these products are used primarily 
in the United States and Europe with a small percentage in Asia.




Specially crafted packets sent to Port 102/TCP (ISO-TSAP) or via Profibus 
could cause the affected device to go into defect mode. A cold restart is 
required to recover the system.

CVE-2015-2177[b] has been assigned to this vulnerability. A CVSS v2 base score 
of 7.8 has been assigned; the CVSS vector string is 



This vulnerability could be exploited remotely.


No known public exploits specifically target this vulnerability.


Crafting a working exploit for this vulnerability would be difficult.


Siemens recommends the following mitigations:

Apply protection-level 3 (Read/Write protection),

Apply cell protection concept,[d]

Use VPN for protecting network communication between cells, and

Apply Defense-in-Depth.[e]

For more information on these vulnerabilities and detailed instructions, 
please see Siemens Security Advisory SSA-987029 at the following location:


ICS-CERT encourages asset owners to take additional defensive measures to 
protect against this and other cybersecurity risks.

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.

ICS-CERT also provides a section for control systems security recommended 
practices on the ICS-CERT web page at: 
http://ics-cert.us-cert.gov/content/recommended-practices. Several recommended
practices are available for reading and download, including Improving 
Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies. 
ICS-CERT reminds organizations to perform proper impact analysis and risk 
assessment prior to deploying defensive measures.

Additional mitigation guidance and recommended practices are publicly 
available in the ICS-CERT Technical Information Paper, 
ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation 
Strategies, that is available for download from the ICS-CERT web site 

Organizations observing any suspected malicious activity should follow their 
established internal procedures and report their findings to ICS-CERT for 
tracking and correlation against other incidents.

In addition, ICS-CERT recommends that users take the following measures to 
protect themselves from social engineering attacks:

Do not click web links or open unsolicited attachments in email messages.

Refer to Recognizing and Avoiding Email Scams[f] for more information on 
avoiding email scams.

Refer to Avoiding Social Engineering and Phishing Attacks[g] for more 
information on social engineering attacks.

a. CWE-404: Improper Resource Shutdown or Release, 
http://cwe.mitre.org/data/definitions/404, web site last accessed March 05, 

b. NVD, http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-2177, NIST 
uses this advisory to create the CVE web site report. This web site will be 
active sometime after publication of this advisory.

c. CVSS Calculator, 
http://nvd.nist.gov/cvss.cfm?version=2&vector=AV:N/AC:L/Au:N/C:N/I:N/A:C, web
site last accessed March 05, 2015.

d. Operational Guidelines for Industrial Security, 
https://www.siemens.com/cert/operational-guidelines-industrial-security, web 
site last accessed March 05, 2015.

e. Further information about Defense-in-Depth, 
web site last accessed March 05, 2015.

f. Recognizing and Avoiding Email Scams, 
http://www.us-cert.gov/reading_room/emailscams_0905.pdf, web site last 
accessed March 05, 2015.

g. National Cyber Alert System Cyber Security Tip ST04-014, 
http://www.us-cert.gov/cas/tips/ST04-014.html, web site last accessed March 
05, 2015.

Contact Information

For any questions related to this report, please contact ICS-CERT at:

Email: ics-cert@hq.dhs.gov

Toll Free: 1-877-776-7585

International Callers: (208) 526-0900

For industrial control systems security information and incident reporting: 

ICS-CERT continuously strives to improve its products and services. You can 
help by choosing one of the links below to provide feedback about this 

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