How severe is CVE-2020-35685?

CVE-2020-35685 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2020-35685 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (79th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-35685?

CVE-2020-35685 primarily affects Hcc-embedded Nichestack. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-35685?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2020-35685 published?

CVE-2020-35685 was published on 2021-08-19 and last updated on 2026-06-17.

CVE-2020-35685

CVE-2020-35685 is a critical-severity vulnerability in Hcc-embedded Nichestack with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-330.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 6.4
EPSS exploit prediction: 2% (79th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-330
Affected product: Hcc-embedded Nichestack
Published: 2021-08-19
Last modified: 2026-06-17

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.)

Frequently asked questions

What is CVE-2020-35685?: 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.)
How severe is CVE-2020-35685?: CVE-2020-35685 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2020-35685 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (79th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-35685?: CVE-2020-35685 primarily affects Hcc-embedded Nichestack. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-35685?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2020-35685 published?: CVE-2020-35685 was published on 2021-08-19 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:a:hcc-embedded:nichestack:3.0:*:*:*:*:*:*:*
cpe:2.3:o:siemens:sentron_3wa_com190_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:siemens:sentron_3wl_com35_firmware:*:*:*:*:*:*:*:*

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