HOMEVULNERABILITIESCVE-2020-35685
CRITICAL

CVE-2020-35685

CWE-330Published: August 19, 2021· Updated: Jun 17, 2026

9.1
CVSS v3.1

Official Description

An issue was discovered in HCC Nichestack 3.0. The code that generates Initial Sequence Numbers (ISNs) for TCP connections derives the ISN from an insufficiently random source. As a result, an attacker may be able to determine the ISN of current and future TCP connections and either hijack existing ones or spoof future ones. (Proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.)

NVD Source

Technical Analysis

CVE-2020-35685 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), with a CVSS base score of 9.1.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected Vendors & Products

hcc-embedded1 product(s)
nichestack
siemens4 product(s)
sentron 3wa com190 firmwaresentron 3wa com190sentron 3wl com35 firmwaresentron 3wl com35
Source: NVD CPE · 5 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://cert-portal.siemens.com/productcert/pdf/ssa-789208.pdf
ADVISORYhttps://www.forescout.com/blog/new-critical-operational-technology-vulnerabilities-found-on-nichestack/
ADVISORYhttps://www.kb.cert.org/vuls/id/608209
ADVISORYhttps://cert-portal.siemens.com/productcert/pdf/ssa-789208.pdf
ADVISORYhttps://www.forescout.com/blog/new-critical-operational-technology-vulnerabilities-found-on-nichestack/
ADVISORYhttps://www.kb.cert.org/vuls/id/608209

All References (8)

→
https://cert-portal.siemens.com/productcert/pdf/ssa-789208.pdfMitigation · Third Party Advisory
→
https://www.forescout.com/blog/new-critical-operational-technology-vulnerabilities-found-on-nichestack/Mitigation · Third Party Advisory
→
https://www.hcc-embedded.comProduct
→
https://www.kb.cert.org/vuls/id/608209Third Party Advisory · US Government Resource
→
https://cert-portal.siemens.com/productcert/pdf/ssa-789208.pdfMitigation · Third Party Advisory
→
https://www.forescout.com/blog/new-critical-operational-technology-vulnerabilities-found-on-nichestack/Mitigation · Third Party Advisory
→
https://www.hcc-embedded.comProduct
→
https://www.kb.cert.org/vuls/id/608209Third Party Advisory · US Government Resource

Quick Facts

CVE IDCVE-2020-35685
CVSS Score9.1 / 10
SeverityCRITICAL
WeaknessCWE-330
CISA KEVNo
Affected2 vendor(s)
PublishedAug 19, 2021

Related CVEs (CWE-330)

CVE-2020-27631
9.8
CVE-2026-27637
9.8
CVE-2021-23451
9.8
CVE-2022-36536
9.8
CVE-2021-28024
9.8
CVE-2023-29332
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2020-35685 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
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