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AUSCERT External Security Bulletin Redistribution
Advisory (icsa-21-257-10) Siemens SIPROTEC 5 relays
15 September 2021
AusCERT Security Bulletin Summary
Product: Siemens SIPROTEC 5 relays
Operating System: Network Appliance
Impact/Access: Execute Arbitrary Code/Commands -- Remote/Unauthenticated
Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-33720 CVE-2021-33719
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ICS Advisory (ICSA-21-257-10)
Siemens SIPROTEC 5 relays
Original release date: September 14, 2021
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1. EXECUTIVE SUMMARY
o CVSS v3 9.8
o ATTENTION: Exploitable remotely/low attack complexity
o Vendor: Siemens
o Equipment: SIPROTEC 5 relays
o Vulnerabilities: Classic Buffer Overflow
2. RISK EVALUATION
Successful exploitation of these vulnerabilities could allow an attacker to
cause a denial-of-service condition or trigger a remote code execution.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
The following versions of SIPROTEC 5 relays are affected:
o SIPROTEC 5 relays with CPU variants CP050: All versions prior to 8.80
o SIPROTEC 5 relays with CPU variants CP100: All versions prior to 8.80
o SIPROTEC 5 relays with CPU variants CP150: All versions
o SIPROTEC 5 relays with CPU variants CP200: All versions
o SIPROTEC 5 relays with CPU variants CP300: All versions prior to 8.80
3.2 VULNERABILITY OVERVIEW
3.2.1 BUFFER COPY WITHOUT CHECKING SIZE OF INPUT ('CLASSIC BUFFER OVERFLOW')
An attacker can send specially crafted packets to Port 4443/TCP, which may
cause a denial-of-service condition or a remote code execution.
CVE-2021-33719 has been assigned to this vulnerability. A CVSS v3 base score of
9.8 has been calculated; the CVSS vector string is ( AV:N/AC:L/PR:N/UI:N/S:U/
3.2.2 BUFFER COPY WITHOUT CHECKING SIZE OF INPUT ('CLASSIC BUFFER OVERFLOW')
An attacker can send specially crafted packets to Port 4443/TCP, which may
cause a denial-of-service condition.
CVE-2021-33720 has been assigned to this vulnerability. A CVSS v3 base score of
5.3 has been calculated; the CVSS vector string is ( AV:N/AC:L/PR:N/UI:N/S:U/
o CRITICAL INFRASTRUCTURE SECTORS: Energy
o COUNTRIES/AREAS DEPLOYED: Worldwide
o COMPANY HEADQUARTERS LOCATION: Germany
Michael Messner from Siemens Energy reported these vulnerabilities to Siemens.
Siemens has released updates for the following products:
o SIPROTEC 5 relays with CPU variants CP050, CP100, or CP300: Update to v8.80
or later .
Siemens has identified the following specific workarounds and mitigations users
can apply to reduce the risk:
o Block access to Port 4443/TCP, such as with an external firewall.
Siemens notes operators of critical power systems (e.g., TSOs or DSOs)
worldwide are usually required by regulations to build resilience into the
power grids by applying multi-level redundant secondary protection schemes.
Therefore, Siemens recommends the operators check whether appropriate resilient
protection measures are in place. The risk of cyber incidents impacting the
grid's reliability can thus be minimized by virtue of the grid design.
Siemens strongly recommends applying the provided security updates using the
corresponding tooling and documented procedures made available with the
product. If supported by the product, an automated means to apply the security
updates across multiple product instances may be used. Siemens strongly
recommends prior validation of any security update before being applied, and
supervision, by trained staff, of the update process in the target environment.
As a general security measure Siemens strongly recommends protecting network
access with appropriate mechanisms (e.g., firewalls, segmentation, VPN) and
advises to configure the environment according to their operational guidelines
in order to run the devices in a protected IT environment.
Additional information on industrial security by Siemens can be found at:
Please see Siemens Security Advisory SSA-847986 for more information.
CISA 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 VPNs may have vulnerabilities and should be
updated to the most current version available. Also recognize VPN is only
as secure as its connected devices.
CISA reminds organizations to perform proper impact analysis and risk
assessment prior to deploying defensive measures.
CISA also provides a section for control systems security recommended practices
on the ICS webpage on us-cert.cisa.gov . 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 webpage on us-cert.cisa.gov 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 CISA for tracking
and correlation against other incidents.
No known public exploits specifically target these vulnerabilities.
For any questions related to this report, please contact the CISA at:
Toll Free: 1-888-282-0870
CISA continuously strives to improve its products and services. You can help by
choosing one of the links below to provide feedback about this product.
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