CVE-2020-27213

HIGHNVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2023-10-10. NVD baseline CVSS 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 7.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

An issue was discovered in Ethernut Nut/OS 5.1. 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. While the ISN generator seems to adhere to RFC 793 (where a global 32-bit counter is incremented roughly every 4 microseconds), proper ISN generation should aim to follow at least the specifications outlined in RFC 6528.

CVSS v3
7.5
EG Score
7.5(medium)
EG Risk
—
EPSS
58.3%
KEV
Not listed

Published

October 10, 2023

Last Modified

November 21, 2024

References (8)

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 42× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 22:38 UTCEG score recompute
  2. 2026-07-22 14:05 UTCEPSS rescore
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  60. 2026-05-24 16:13 UTCEG score recompute
  61. 2026-05-24 16:13 UTCGHSA enrichment
  62. 2026-05-23 15:05 UTCOSV refresh

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2020-27213?
CVE-2020-27213 is a high vulnerability published on October 10, 2023. An issue was discovered in Ethernut Nut/OS 5.1. 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…
When was CVE-2020-27213 disclosed?
CVE-2020-27213 was first published in the National Vulnerability Database on October 10, 2023, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-27213 actively exploited?
CVE-2020-27213 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 58.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2020-27213?
CVE-2020-27213 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2020-27213?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-27213, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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