5 Medium
CVSS2
Attack Vector
NETWORK
Attack Complexity
LOW
Authentication
NONE
Confidentiality Impact
NONE
Integrity Impact
PARTIAL
Availability Impact
NONE
AV:N/AC:L/Au:N/C:N/I:P/A:N
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
8.4 High
AI Score
Confidence
Low
0.002 Low
EPSS
Percentile
51.6%
CISA is aware of a public report, known as βNUMBER:JACKβ that details vulnerabilities found in multiple open-source and proprietary TCP/IP stacks. CISA is issuing this advisory to provide early notice of the reported vulnerabilities and identify baseline mitigations for reducing risks to these and other cybersecurity attacks.
The various open-source stacks may be implemented in forked repositories.
This updated advisory is a follow-up to the advisory update titled ICSA-21-042-01 Multiple Embedded TCP/IP stacks (Update A) that was published February 18, 2021, to the ICS webpage on us-cert.cisa.gov.
Successful exploitation of weak initial sequence numbers (ISN) can be used to hijack or spoof TCP connections, cause denial-of-service conditions, inject malicious data, or bypass authentication.
The following have been reported to be affected:
--------- Begin Update B Part 1 of 2 ---------
--------- End Update B Part 1 of 2 ---------
Nut/Net software relies on highly predictable source values and has consistent increments when generating initial sequence numbers (ISN), which may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27213 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:H/A:N).
uC/TCP-IP ISN generation relies on a linear congruential generator (LCG), which is reversable from observed output streams as the algorithm is seeded with publicly recoverable information. This defect may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27630 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:H/A:N).
CycloneTCP ISN generation relies on a linear congruential generator (LCG), which is reversable from observed output streams as the algorithm is seeded with publicly recoverable information. This defect may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27631 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:H/A:N).
NDKTCPIP software is initialized with a consistent value and has consistent increments when generating initial sequence numbers (ISN), which may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27632 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:H/A:N).
FNET software is initialized with a consistent value and has consistent increments when generating initial sequence numbers (ISN), which may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27633 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:H/A:N).
uIP, Contiki-OS, and Contiki-NG software is initialized with a consistent value and has consistent increments when generating initial sequence numbers (ISN), which may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27634 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:H/A:N).
PicoTCP PicoTCP-NG software ISN generation relies on a linear congruential generator (LCG), which is reversable from observed output streams as the algorithm is seeded with publicly recoverable information. This defect may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27635 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:H/A:N).
MPLAB software ISN generation relies on a linear congruential generator (LCG), which is reversable from observed output streams as the algorithm is seeded with publicly recoverable information. This defect may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-27636 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:H/A:N).
Nucleus NET and Nucleus ReadyStart software ISN generation relies on a combination of values that can be acquired from capturing network traffic, which may allow an attacker to spoof or disrupt TCP connections.
CVE-2020-28388 has been assigned to this vulnerability. A CVSS v3 base score of 6.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L).
Daniel dos Santos, Stanislav Dashevskyi, Jos Wetzels, and Amine Amri of Forescout Research Labs reported these vulnerabilities to CISA.
--------- Begin Update B Part 2 of 2 ---------
--------- End Update B Part 2 of 2 ---------
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-12-146-01BβTargeted 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-2020-27213
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27630
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27631
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27632
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27633
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27634
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27635
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-27636
web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-28388
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
cwe.mitre.org/data/definitions/330.html
github.com/butok/FNET/releases/tag/v4.7.1
github.com/Microchip-MPLAB-Harmony/net/security/advisories/GHSA-2q6g-59x4-pwx6
github.com/Oryx-Embedded/CycloneTCP/commit/248b6e2063906d2c98a096d235cb008424d72fa6
github.com/virtualsquare/picotcp/pull/3
public.govdelivery.com/accounts/USDHSCISA/subscriber/new?topic_id=USDHSCISA_138
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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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mailto:?subject=Multiple%20Embedded%20TCP/IP%20Stacks%20%28Update%20B%29&body=www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
5 Medium
CVSS2
Attack Vector
NETWORK
Attack Complexity
LOW
Authentication
NONE
Confidentiality Impact
NONE
Integrity Impact
PARTIAL
Availability Impact
NONE
AV:N/AC:L/Au:N/C:N/I:P/A:N
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
8.4 High
AI Score
Confidence
Low
0.002 Low
EPSS
Percentile
51.6%