CVE-2021-27393

Name: CVE-2021-27393
Creator: NVD / NIST
Published: 2021-04-22T21:15:10.393+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.75%

Last modified Jun 17, 2026

CVE-2021-27393 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. A vulnerability has been identified in Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2013.08), Nucleus Source Code (Versions including affected DNS modules). The DNS client does not properly randomize UDP port numbers of DNS requests. EPSS estimates a 0.75% chance of exploitation in the next 30 days.

Description

A vulnerability has been identified in Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2013.08), Nucleus Source Code (Versions including affected DNS modules). The DNS client does not properly randomize UDP port numbers of DNS requests. That could allow an attacker to poison the DNS cache or spoof DNS resolving.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.75%

50.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Siemens	Nucleus Net	All versions
Siemens	Nucleus Readystart V3	< 2013.08
Siemens	Nucleus Source Code	All versions

References

https://cert-portal.siemens.com/productcert/pdf/ssa-201384.pdfVendor Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-201384.pdfVendor Advisory

Timeline

Published: Apr 22, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-27393?

How severe is CVE-2021-27393?

CVE-2021-27393 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.75% probability of exploitation in the next 30 days.

How do I fix CVE-2021-27393?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-27393?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST