CVSS2
Attack Vector
NETWORK
Attack Complexity
LOW
Authentication
NONE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:L/Au:N/C:P/I:P/A:P
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
AI Score
Confidence
High
EPSS
Percentile
79.6%
This updated advisory is a follow-up to the original advisory titled ICSA-21-040-05 Siemens SIMATIC SmartVNC HMI WinCC Products that was published September 14, 2021, to the ICS webpage on us-cert.cisa.gov.
Successful exploitation of these vulnerabilities could allow remote code execution, information disclosure and denial-of-service attacks under certain conditions.
The following Siemens SIMATIC HMIs/WinCC products are affected:
--------- Begin Update A Part 1 of 2 ---------
--------- End Update A Part 1 of 2 ---------
SmartVNC has an out-of-bounds memory access vulnerability that could be triggered on the server side when sending data from the client, which could result in a denial-of-service condition.
CVE-2021-25660 has been assigned to this vulnerability. A CVSS v3 base score of 5.4 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:N/A:H).
SmartVNC has an out-of-bounds memory access vulnerability that could be triggered on the client side when sending data from the server, which could result in a denial-of-service condition.
CVE-2021-25661 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H).
SmartVNC client fails to handle an exception properly if the program execution process is modified after sending a packet from the server, which could result in a denial-of-service condition.
CVE-2021-25662 has been assigned to this vulnerability. A CVSS v3 base score of 5.9 has been calculated; the CVSS vector string is (AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:H).
SmartVNC has a heap allocation leak vulnerability in the server Tight encoder, which could result in a denial-of-service condition.
CVE-2021-27383 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).
SmartVNC has an out-of-bounds memory access vulnerability in the device layout handler represented by a binary data stream on client side, which could result in code execution.
CVE-2021-27384 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/C:H/I:H/A:H).
A remote attacker could send specially crafted packets to a SmartVNC device layout handler on the client side, which could influence the number of resources consumed and result in a denial-of-service condition (infinite loop).
CVE-2021-27385 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).
SmartVNC has a heap allocation leak vulnerability in the device layout handler on client side, which could result in a denial-of-service condition.
CVE-2021-27386 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).
Siemens reported these vulnerabilities to CISA.
Siemens recommends applying updates where available:
--------- Begin Update A Part 2 of 2 ---------
--------- End Update A Part 2 of 2 ---------
Siemens has identified the following specific workarounds and mitigations users can apply to reduce the risk:
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 the [Siemens operational guidelines for industrial security](<https://cert-portal.siemens.com/operational-guidelines-industrial-security.pdf >) and following the recommendations in the product manuals.
For additional information, please refer to Siemens Security Advisory SSA-538778
CISA recommends users take defensive measures to minimize the risk of exploitation of these vulnerabilities. Specifically, users should:
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 Strategies.
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. These vulnerabilities have a high attack complexity.
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-25660
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-25661
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-25662
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-27383
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-27384
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-27385
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-27386
cert-portal.siemens.com/operational-guidelines-industrial-security.pdf
cert-portal.siemens.com/productcert/pdf/ssa-538778.pdf
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us-cert.cisa.gov/ics/tips/ICS-TIP-12-146-01B
us-cert.cisa.gov/sites/default/files/recommended_practices/NCCIC_ICS-CERT_Defense_in_Depth_2016_S508C.pdf
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CVSS2
Attack Vector
NETWORK
Attack Complexity
LOW
Authentication
NONE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:L/Au:N/C:P/I:P/A:P
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
AI Score
Confidence
High
EPSS
Percentile
79.6%