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

Q: How do I fix CVE-2020-35685?

nichestack: downgrade or apply the listed mitigation; sentron 3wa com190 firmware: upgrade to 2.0.0; sentron 3wl com35 firmware: upgrade to 1.2.0. Exact commands for each OS are on this page.

Q: Is CVE-2020-35685 being exploited?

CVE-2020-35685 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-35685 affect?

CVE-2020-35685 affects nichestack, sentron 3wa com190 firmware, sentron 3wl com35 firmware. Severity is critical (CVSS 9.1). 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 cu

Q: How urgent is CVE-2020-35685?

Priority 57/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.1REMOTEDOWNGRADEUPGRADEUPGRADE

CVE-2020-35685 is a critical-severity flaw (CVSS 9.1) affecting nichestack, sentron 3wa com190 firmware, sentron 3wl com35 firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.)

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.1% (top 19%)
CISA exploited list	No
Weakness	CWE-330
Published	2021-08-19
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: hcc-embedded · siemens

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-19 12:15 UTCPublished CVE record published
2026-06-17 03:14 UTCUpdated Record last modified

hcc-embedded nichestack DOWNGRADE

Affected: 3.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.0

1. Check installed version

apt-cache policy nichestack || rpm -q nichestack || nichestack --version

2. No fixed release: DOWNGRADE to a release before 3.0 (Debian / Ubuntu)

apt-cache madison nichestack sudo apt install nichestack=<VERSION_BEFORE_3.0> sudo apt-mark hold nichestack

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list nichestack sudo dnf downgrade nichestack-<VERSION_BEFORE_3.0> sudo dnf versionlock add nichestack

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

siemens sentron 3wa com190 firmware UPGRADE

Affected: < 2.0.0

Fixed in: 2.0.0

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

siemens sentron 3wl com35 firmware UPGRADE

Affected: < 1.2.0

Fixed in: 1.2.0

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-35685?

nichestack: downgrade or apply the listed mitigation; sentron 3wa com190 firmware: upgrade to 2.0.0; sentron 3wl com35 firmware: upgrade to 1.2.0. Exact commands for each OS are on this page.

Is CVE-2020-35685 being exploited?

CVE-2020-35685 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-35685 affect?

CVE-2020-35685 affects nichestack, sentron 3wa com190 firmware, sentron 3wl com35 firmware. Severity is critical (CVSS 9.1). 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 cu

How urgent is CVE-2020-35685?

Priority 57/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Siemens vulnerabilities

Related CVEs

CVE-2021-36762 HIGH 7.5 UPGRADE An issue was discovered in HCC Embedded InterNiche NicheStack through 4.3
CVE-2021-31401 HIGH 7.5 UPGRADE UPGRADE An issue was discovered in tcp_rcv() in nptcp.c in HCC embedded InterNiche 4.0.1
CVE-2021-31400 HIGH 7.5 UPGRADE An issue was discovered in tcp_pulloutofband() in tcp_in.c in HCC embedded InterNiche 4.0.1
CVE-2021-31228 HIGH 7.5 UPGRADE An issue was discovered in HCC embedded InterNiche 4.0.1
CVE-2021-31227 HIGH 7.5 UPGRADE An issue was discovered in HCC embedded InterNiche 4.0.1

References

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