CVE-2020-27630: In Silicon Labs uC/TCP-IP 3.6.0, TCP ISNs are improperly random.

This month

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2020-27630 is a critical-severity flaw (CVSS 9.8) affecting uc\/tcp-ip. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In Silicon Labs uC/TCP-IP 3.6.0, TCP ISNs are improperly random.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.1% (top 35%)
CISA exploited list	No
Weakness	CWE-330
Published	2023-10-10
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: silabs

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

Am I affected?

Timeline

2023-10-10 17:15 UTCPublished CVE record published
2026-06-17 03:09 UTCUpdated Record last modified

silabs uc\/tcp-ip DOWNGRADE

Affected: 3.6.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.6.0

1. Check installed version

apt-cache policy uctcp-ip || rpm -q uctcp-ip || uctcp-ip --version

2. No fixed release: DOWNGRADE to a release before 3.6.0 (Debian / Ubuntu)

apt-cache madison uctcp-ip sudo apt install uctcp-ip=<VERSION_BEFORE_3.6.0> sudo apt-mark hold uctcp-ip

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

dnf --showduplicates list uctcp-ip sudo dnf downgrade uctcp-ip-<VERSION_BEFORE_3.6.0> sudo dnf versionlock add uctcp-ip

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.

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-2020-27630?

uc\/tcp-ip: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-27630 being exploited?

CVE-2020-27630 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-2020-27630 affect?

CVE-2020-27630 affects uc\/tcp-ip. Severity is critical (CVSS 9.8). In Silicon Labs uC/TCP-IP 3.6.0, TCP ISNs are improperly random.

How urgent is CVE-2020-27630?

Priority 56/100. Critical severity; Remotely exploitable, no login, no user action

References

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