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# SSA-116379: Denial-of-Service Vulnerability in OSPF Packet Handling of SCALANCE
XM-400 and XR-500 Devices

Publication Date:        2021-05-11
Last Update:             2021-05-11
Current Version:         1.0
CVSS v3.1 Base Score:    7.5

SUMMARY
=======

SCALANCE XM-400 and XR-500 devices contain a vulnerability in the OSPF
protocol implementation that could allow an unauthenticated remote
attacker to create a permanent denial-of-service condition.

Siemens has released updates for the affected products and recommends to
update to the latest versions.


AFFECTED PRODUCTS AND SOLUTION
==============================


* SCALANCE XM-400 Family 
  - Affected versions:
       All versions < V6.4
  - Remediation:
       Update to V6.4 or later version
  - Download:
       https://support.industry.siemens.com/cs/ww/en/view/109796319/

* SCALANCE XR-500 Family 
  - Affected versions:
       All versions < V6.4
  - Remediation:
       Update to V6.4 or later version
  - Download:
       https://support.industry.siemens.com/cs/ww/en/view/109796317/


WORKAROUNDS AND MITIGATIONS
===========================

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

* Disable OSPF in the layer 3 configuration menu (note that OSPF is
disabled by default). The vulnerability is not exploitable, when OSPF is
disabled.

* If OSPF is used, set a password for the OSPF interface and enable MD5
authentication



GENERAL SECURITY RECOMMENDATIONS
================================

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

Additional information on Industrial Security by Siemens can be found
at: https://www.siemens.com/industrialsecurity

PRODUCT DESCRIPTION
===================

SCALANCE X switches are used to connect industrial components like
Programmable Logic Controllers (PLCs) or Human Machine Interfaces
(HMIs).

VULNERABILITY CLASSIFICATION
============================

The vulnerability classification has been performed by using the CVSS scoring
system in version 3.1 (CVSS v3.1) (https://www.first.org/cvss/). The CVSS
environmental score is specific to the customer's environment and will impact
the overall CVSS score. The environmental score should therefore be
individually defined by the customer to accomplish final scoring.

An additional classification has been performed using the CWE classification, a
community-developed list of common software security weaknesses. This serves as
a common language and as a baseline for weakness identification, mitigation,
and prevention efforts. A detailed list of CWE classes can be found at:
https://cwe.mitre.org/.



* Vulnerability CVE-2020-28393

  The OSPF protocol implementation in affected devices incorrectly handles
  the number of LSA fields in combination with other modified fields.
  
  An unauthenticated remote attacker could create a permanent
  denial-of-service condition by sending specially crafted OSPF packets.
  Successful exploitation requires OSPF to be enabled on an affected
  device.

  CVSS v3.1 Base Score: 7.5
  CVSS Vector:          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:P/RL:O/RC:C
  CWE:                  CWE-682: Incorrect Calculation




ADDITIONAL INFORMATION
======================
All SCALANCE XM-400 and XR-500 devices are affected, including those who
do not support layer 3 routing and OSPF natively, as the activation of
these features is possible via the KEY-PLUG modules:

- -   KEY-PLUG for XM-400:
    https://mall.industry.siemens.com/mall/en/de/Catalog/Product/6GK5904-0PA00
- -   KEY-PLUG for XR-500:
    https://mall.industry.siemens.com/mall/en/de/Catalog/Product/6GK5905-0PA00

As long as layer 3 routing including OSPF is not enabled, the
vulnerability is not exploitable.

For further inquiries on security vulnerabilities in Siemens products and
solutions, please contact the Siemens ProductCERT:

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


HISTORY DATA
============

V1.0 (2021-05-11): Publication Date

TERMS OF USE
============

Siemens Security Advisories are subject to the terms and conditions contained
in Siemens' underlying license terms or other applicable agreements previously
agreed to with Siemens (hereinafter "License Terms"). To the extent applicable
to information, software or documentation made available in or through a
Siemens Security Advisory, the Terms of Use of Siemens' Global Website
(https://www.siemens.com/terms_of_use, hereinafter "Terms of Use"), in
particular Sections 8-10 of the Terms of Use, shall apply additionally. In case
of conflicts, the License Terms shall prevail over the Terms of Use.
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