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Fencer Vulns
medium 5.3

CVE-2021-27393 json

A vulnerability has been identified in Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions < V2013.08), Nucleus Source Code (Ve…

published 2021-04-22 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-14148

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

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.

Patch / fix

  • siemens nucleus_readystart_v3 2013.08

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

cisa ICSA-21-103-14 updated cvss 5.3

Siemens Nucleus DNS (Update A)

  • Siemens Nucleus NET
    affected: mitigation, no fix planned
  • Siemens Nucleus ReadyStart V3 <V2013.08
    affected: fixed in V2013.08, mitigation support.sw.siemens.com
  • Siemens Nucleus Source Code including_affected_DNS_modules
    affected: vendor fix, mitigation

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.75% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:P/A:N

Affected products

  • Siemens Nucleus NET
  • Siemens Nucleus ReadyStart V3
  • Siemens Nucleus Source Code

Classification

Weakness
  • CWE-330 Use of Insufficiently Random Values

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.