1. EXECUTIVE SUMMARY

• CVSS v3 8.1
• ATTENTION: Exploitable remotely/low skill level to exploit.
• Vendor: Siemens
• Equipment: SCALANCE W1750D, M800, and S615
• Vulnerabilities: Resource Exhaustion, Improper Restriction of Operations within the Bounds of a Memory Buffer

2. UPDATE INFORMATION

This updated advisory is a follow-up to the updated advisory titled ICSA-17-332-01 Siemens SCALANCE W1750D, M800, and S615 that was published April 5, 2018, on the NCCIC/ICS-CERT website.

3. RISK EVALUATION

Successful exploitation of these vulnerabilities could allow a remote attacker to crash the DNS service or execute arbitrary code by crafting malicious DNS responses.

4. TECHNICAL DETAILS

4.1 AFFECTED PRODUCTS

The following versions of SCALANCE, network interfaces, are affected:

• SCALANCE W1750D: All versions, and
• SCALANCE M800/S615: All versions.

4.2 VULNERABILITY OVERVIEW

4.2.1 UNCONTROLLED RESOURCE CONSUMPTION ('RESOURCE EXHAUSTION') CWE-400

An attacker can cause a crash of the DNSmasq process by sending specially-crafted request messages to the service.

The following CVEs have been assigned to this group of vulnerabilities:

CVE-2017-13704

CVE-2017-14495

CVE-2017-14496

A CVSS v3 base score of 5.3 has been assigned; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

4.2.2 IMPROPER RESTRICTION OF OPERATIONS WITHIN THE BOUNDS OF A MEMORY BUFFER CWE-119

An attacker can cause a crash or potentially execute arbitrary code by sending specially-crafted DNS responses to the DNSmasq process. In order to exploit this vulnerability, an attacker must be able to trigger DNS requests from the device, and must be in a position that allows the injection of malicious DNS responses.

CVE-2017-14491 has been assigned to this vulnerability. A CVSS v3 base score of 8.1 has been assigned; the CVSS vector string is (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H).

4.3 BACKGROUND

• Critical Infrastructure Sectors: Chemical, Energy, Food and Agriculture, Healthcare and Public Health, Transportation Systems, and Water and Wastewater Systems
• Countries/Areas Deployed: Worldwide
• Company Headquarters Location: Germany

4.4 RESEARCHER

Siemens Product CERT reported the vulnerabilities to NCCIC.

5. MITIGATIONS

Siemens reports they are preparing updates for the affected products and recommends the following mitigations until patches are available:

• For SCALANCE W1750D: Siemens recommends that users install V6.5.1.5-4.3.1.8 of the software. Users who do not use the “OpenDNS,” “Captive Portal,” or “URL redirection” functionalities can deploy firewall rules in the device configuration to block incoming access to Port 53/UDP.

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• For SCALANCE M800/S615: Siemens recommends that users install V5.0 of the software. Alternatively, users can disable DNS proxy in the device configuration (System - DNS - DNS Proxy - Disable Checkbox for Enable DNS Proxy) and configure the connected devices in the internal network to use a different DNS server.

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• Apply Defense-in-Depth

Siemens has produced an advisory that can be found at:

https://www.siemens.com/cert/pool/cert/siemens_security_advisory_ssa-689071.pdf

Siemens also reports that SCALANCE W1750D devices that are operated in controller mode on an Aruba Mobility Controller are not affected if AOS versions newer than V6.3.1.25, V6.4.4.16 V6.5.1.9, V6.5.3.3, V6.5.4.2, or 8.1.0.4 are used.

NCCIC recommends users take defensive measures to minimize the risk of exploitation of these vulnerabilities. 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 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 these vulnerabilities.