PatchTheCVECVE-2020-27213: An issue was discovered in Ethernut Nut/OS 5.1
CVE-2020-27213 is a high-severity flaw (CVSS 7.5) affecting nut\/os. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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 microseco
Why this priority
- High severity
- Public exploit reference
- Remotely exploitable, no login, no user action
No fix is published yet: follow the downgrade or mitigation steps.
Risk facts
| CVSS score | 7.5 (High) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 1.0% (top 38%) |
| CISA exploited list | No |
| Weakness | CWE-330 |
| Published | 2023-10-10 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
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-2020-27213?
nut\/os: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2020-27213 being exploited?
CVE-2020-27213 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-2020-27213 affect?
CVE-2020-27213 affects nut\/os. Severity is high (CVSS 7.5). 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 c
How urgent is CVE-2020-27213?
Priority 52/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action