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CVE Record

CVE-2020-35685: An issue was discovered in HCC Nichestack 3.0.

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.)

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw weakens how HCC NicheStack 3.0 creates TCP connection numbers. If an attacker can observe or predict them, they may be able to impersonate or interfere with TCP sessions. The business risk is highest for embedded or operational technology devices that expose affected network services.

Executive priority

Prioritize asset identification first. The vulnerability can affect trust in TCP sessions, but product mapping and fix details are incomplete in the provided sources. Focus urgent effort on exposed OT or embedded systems where disruption or unauthorized control would be material.

Technical view

CVE-2020-35685 is insufficient randomness in TCP Initial Sequence Number generation in HCC NicheStack 3.0. The CVE states attackers may determine current and future ISNs, enabling TCP session hijacking or spoofing. Sources cite RFC 6528 as the expected ISN generation benchmark.

Likely exposure

Likely exposure is embedded products or OT devices using HCC NicheStack 3.0. The CVE bundle does not identify specific affected OEM products, versions, or CPEs. Siemens and CERT advisories should be used to map vendor-specific impact.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. Exploitation would require network conditions that allow practical ISN prediction and useful access to target TCP sessions. Treat internet-exposed or poorly segmented OT networks as higher risk.

Researcher notes

The core weakness is predictable TCP ISN generation, not an application-layer bug. Evidence in the bundle is enough to justify exposure review, but not enough to name affected downstream products or active exploitation. Validate through vendor/OEM firmware lineage rather than assumptions.

Mitigation direction

  • Check HCC, Siemens, CERT, and OEM guidance for fixed firmware or stack updates.
  • Inventory devices and firmware that embed HCC NicheStack 3.0.
  • Restrict affected TCP services to trusted management networks only.
  • Segment OT and embedded networks from internet and corporate access paths.
  • Monitor vendor advisories for product-specific fixes and compensating controls.

Validation and detection

  • Confirm whether device SBOMs, firmware notes, or OEM advisories mention HCC NicheStack 3.0.
  • Map exposed TCP services on devices suspected to use the affected stack.
  • Verify whether vendor firmware has incorporated an HCC NicheStack fix.
  • Review firewall rules limiting access to affected device TCP services.
  • Check logs for unusual TCP session resets, spoofing indicators, or unexpected source hosts.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2020-35685 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
5Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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