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.)

Published: 2021-08-19 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-35685 is rated Moderate Risk (57/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 0.41%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-35685

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-03-30 0.26% 0.41% +0.15%
2 2025-03-29 0.41% 0.26% -0.15%
3 2025-03-24 — 0.41% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-35685

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.1 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 5.2 [email protected]
6.4 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 4.9 [email protected]

Weakness enumeration for CVE-2020-35685

Affected software / configurations for CVE-2020-35685

Vendor Product Version Raw CPE
hcc-embedded nichestack 3.0 cpe:2.3:a:hcc-embedded:nichestack:3.0:*:*:*:*:*:*:*
siemens sentron_3wa_com190_firmware < 2.0.0 cpe:2.3:o:siemens:sentron_3wa_com190_firmware:*:*:*:*:*:*:*:*
siemens sentron_3wl_com35_firmware < 1.2.0 cpe:2.3:o:siemens:sentron_3wl_com35_firmware:*:*:*:*:*:*:*:*

References for CVE-2020-35685

cvelogic Threat Intelligence