9.8 High
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
9.4 High
AI Score
Confidence
Low
7.5 High
CVSS2
Access Vector
NETWORK
Access 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
0.007 Low
EPSS
Percentile
79.5%
CISA is aware of a public report known as NUCLEUS:13 detailing vulnerabilities found in the TCP/IP stack and related services (FTP, TFTP) of the networking component (Nucleus NET) in the Nucleus Real-Time Operating System (RTOS). CISA is issuing this advisory to provide early notice of these reported vulnerabilities and identify baseline mitigations for reducing risks to these and other cybersecurity attacks.
Successful exploitation of these vulnerabilities could cause a denial-of-service condition, allow an information leakage, or remote code execution.
The following products and versions of the Nucleus RTOS are affected:
ICMP echo packets with fake IP options allow sending ICMP echo reply messages to arbitrary hosts on the network.
CVE-2021-31344 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/C:N/I:L/A:N).
The total length of an UDP payload (set in the IP header) is unchecked. This may lead to various side effects, including information leak and denial-of-service conditions, depending on a user-defined application that runs on top of the UDP protocol.
CVE-2021-31345 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:H/I:N/A:N).
The total length of an ICMP payload (set in the IP header) is unchecked. This may lead to various side effects, including information leak and denial-of-service conditions, depending on the network buffer organization in memory.
CVE-2021-31346 has been assigned to this vulnerability. A CVSS v3 base score of 8.2 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H).
When processing a DHCP OFFER message, the DHCP client application does not validate the length of the vendor option(s), leading to denial-of-service conditions.
CVE-2021-31881 has been assigned to this vulnerability. A CVSS v3 base score of 7.1 has been calculated; the CVSS vector string is (AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H).
The DHCP client application does not validate the length of the domain name server IP option(s) (0x06) when processing DHCP ACK packets. This may lead to denial-of-service conditions.
CVE-2021-31882 has been assigned to this vulnerability. A CVSS v3 base score of 6.5 has been calculated; the CVSS vector string is (AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
When processing a DHCP ACK message, the DHCP client application does not validate the length of the vendor option(s), leading to denial-of-service conditions.
CVE-2021-31883 has been assigned to this vulnerability. A CVSS v3 base score of 7.1 has been calculated; the CVSS vector string is (AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H).
The DHCP client application assumes the data supplied with the “hostname” DHCP option NULL is terminated. In cases when a global hostname variable is not defined, this may lead to out-of-bound reads, out-of-bounds writes, and denial-of-service conditions.
CVE-2021-31884 has been assigned to this vulnerability. A CVSS v3 base score of 8.8 has been calculated; the CVSS vector string is (AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).
TFTP server application allows for reading the contents of the TFTP memory buffer via sending malformed TFTP commands.
CVE-2021-31885 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:H/I:N/A:N).
FTP server does not properly validate the length of the “USER” command, leading to stack-based buffer overflows. This may result in denial-of-service conditions and remote code execution.
CVE-2021-31886 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).
FTP server does not properly validate the length of the “PWD/XPWD” command, leading to stack-based buffer overflows. This may result in denial-of-service conditions and remote code execution.
CVE-2021-31887 has been assigned to this vulnerability. A CVSS v3 base score of 8.8 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).
FTP server does not properly validate the length of the “MKD/XMKD” command, leading to stack-based buffer overflows. This may result in denial-of-service conditions and remote code execution.
CVE-2021-31888 has been assigned to this vulnerability. A CVSS v3 base score of 8.8 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).
Malformed TCP packets with a corrupted SACK option lead to information leaks and denial-of-service conditions.
CVE-2021-31889 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).
The total length of a TCP payload (set in the IP header) is unchecked. This may lead to various side effects, including information leak and denial-of-service conditions, depending on the network buffer organization in memory.
CVE-2021-31890 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).
Daniel dos Santos, Stanislav Dashevskyi, and Amine Amri of Forescout Research Labs, and Uriel Malin and Tal Zohar of Medigate reported these vulnerabilities to CISA.
Siemens has released updates for several of the affected products and recommends updating to the latest versions. Siemens recommends countermeasures for products where updates are not available. Siemens has not identified any additional specific workarounds or mitigations.
As a general security measure, Siemens 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 Siemens’ operational guidelines for industrial security and following the recommendations in the product manuals.
For additional information, please refer to Siemens Security Advisory SSA-044112
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.
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31344
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31345
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31346
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31881
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31882
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31883
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31884
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31885
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31886
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31887
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31888
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31889
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-31890
cert-portal.siemens.com/productcert/pdf/ssa-044112.pdf
cwe.mitre.org/data/definitions/119.html
cwe.mitre.org/data/definitions/119.html
cwe.mitre.org/data/definitions/125.html
cwe.mitre.org/data/definitions/1284.html
cwe.mitre.org/data/definitions/1284.html
cwe.mitre.org/data/definitions/170.html
cwe.mitre.org/data/definitions/170.html
cwe.mitre.org/data/definitions/170.html
cwe.mitre.org/data/definitions/170.html
cwe.mitre.org/data/definitions/191.html
cwe.mitre.org/data/definitions/240.html
cwe.mitre.org/data/definitions/805.html
cwe.mitre.org/data/definitions/843.html
public.govdelivery.com/accounts/USDHSCISA/subscriber/new?topic_id=USDHSCISA_138
support.industry.siemens.com/cs/start?lc=en-US
support.industry.siemens.com/cs/start?lc=en-US
support.industry.siemens.com/cs/start?lc=en-US
support.sw.siemens.com/en-US/product/1009925838/
support.sw.siemens.com/en-US/product/1336134128/
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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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www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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9.8 High
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
9.4 High
AI Score
Confidence
Low
7.5 High
CVSS2
Access Vector
NETWORK
Access 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
0.007 Low
EPSS
Percentile
79.5%