What’s Vulnerable › Vulnerabilities

CVE-2020-35685

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-19 · updated 2026-06-17
• Weakness: CWE-330

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.)

Affected products

• Hcc-Embedded Nichestack: 3.0
• Siemens Sentron 3Wa Com190 Firmware: before 2.0.0 — fixed in 2.0.0
• Siemens Sentron 3Wl Com35 Firmware: before 1.2.0 — fixed in 1.2.0

How to fix

Upgrade to a fixed version: Siemens Sentron 3Wa Com190 Firmware 2.0.0; Siemens Sentron 3Wl Com35 Firmware 1.2.0. Check the vendor advisory for mitigations.

References

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

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