CVE-2021-27393

mediumpriority · track · 21OT risk · elevatedEPSS 0.008 · 55 %ileDEEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.75% (55th) EPSS

CVSS 5 · medium

Is it mine?

19 products

Check your exposure

Who says so?

6 sources

cnnvd · enisa_euvd · cert_bund · cisa_csaf_ot

EPSS · scored 2026-10-27

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.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

A vendor fix is available.

FixedNucleus ReadyStart V3siemens_psirt
Update to V2013.08 or later version
https://support.sw.siemens.com/en-US/product/1009925838/
FixedNucleus Source Codesiemens_psirt
Contact customer support to receive patch and update information
FixedNucleus ReadyStart V3cisa_csaf_ot
Update to V2013.08 or later version
https://support.sw.siemens.com/en-US/product/1009925838/
FixedNucleus Source Codecisa_csaf_ot
Contact customer support to receive patch and update information
MitigationNucleus NETsiemens_psirt
Avoid using DNS client of affected versions
MitigationNucleus ReadyStart V3siemens_psirt
Avoid using DNS client of affected versions
MitigationNucleus Source Codesiemens_psirt
Avoid using DNS client of affected versions
MitigationNucleus NETcisa_csaf_ot
Avoid using DNS client of affected versions
MitigationNucleus ReadyStart V3cisa_csaf_ot
Avoid using DNS client of affected versions
MitigationNucleus Source Codecisa_csaf_ot
Avoid using DNS client of affected versions
No fix plannedNucleus NETsiemens_psirt
Currently no remediation is planned
No fix plannedNucleus NETcisa_csaf_ot
Currently no remediation is planned

cvss

Technical severity, 0–10. One row per scoring source.

5.3

010

base score 0–10 · higher = more severe · hover a vector to decode

v2.05mediumAV:N/AC:L/Au:N/C:N/I:P/A:Nprimary · NVD / NIST USexploitability 10 · impact 2.9

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:Nprimary · NVD / NIST USexploitability 3.9 · impact 1.4

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:Csecondary · CISA US

v3.15.3mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:O/RC:Csecondary · Siemens ProductCERT DE

v3.14.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-330USCWE-330USCWE-330US

affected products (19)

Products and version ranges known to be affected.

Microsoft Azure RTOS NetXall versionscert_bundDEcpe:/o:microsoft:azure_rtos_netx:-
Siemens Nucleus Netall versionscert_bundDEcpe:/a:siemens:nucleus_net:-
Siemens Nucleus RTOSall versionscert_bundDEcpe:/o:siemens:nucleus_rtos:-
Wind River VxWorksall versionscert_bundDEcpe:/o:windriver:vxworks:-
Nucleus NETall versionscisa_csaf_otUS
Nucleus ReadyStart V3all versionscisa_csaf_otUS
Nucleus Source Codeall versionscisa_csaf_otUS
Siemens Nucleus NET≤ vers:all/*cisa_csaf_otUS
Siemens Nucleus ReadyStart V3< V2013.08cisa_csaf_otUS
Siemens Nucleus Source Code≤ including_affected_DNS_modulescisa_csaf_otUS
Siemens Nucleus NET≤ All versionsenisa_euvdEU
Siemens Nucleus ReadyStart V3All versions → V2013.08enisa_euvdEU
Siemens Nucleus Source Code≤ Versions including affected DNS modulesenisa_euvdEU
siemens nucleus netall versionsnvdUScpe:2.3:a:siemens:nucleus_net:*:*:*:*:*:*:*:*
siemens nucleus readystart v3< 2013.08nvdUScpe:2.3:a:siemens:nucleus_readystart_v3:*:*:*:*:*:*:*:*
siemens nucleus source codeall versionsnvdUScpe:2.3:a:siemens:nucleus_source_code:*:*:*:*:*:*:*:*
Siemens Nucleus NET≤ vers:all/*siemens_psirtDE
Siemens Nucleus ReadyStart V3< V2013.08siemens_psirtDE
Siemens Nucleus Source Code≤ Versions including affected DNS modulessiemens_psirtDE

advisories (3)

Vendor and ecosystem advisories describing this.

SSA-201384SSA-201384: Predictable UDP Port Number Vulnerability (NAME:WRECK) in the DNS Module of Nucleus RTOS2021-04-13csaf · siemens_psirtDE
Security researchers discovered and disclosed 9 vulnerabilities in several DNS implementations, also known as “NAME:WRECK” vulnerabilities. The vulnerability described in this advisory is from this set. The DNS client of of the networking component (Nucleus NET) in Nucleus Real-Time Operating System (RTOS) contains a vulnerability related to the handling of UDP port numbers in DNS requests that could allow an attacker to poison the DNS cache or spoof DNS resolving. Siemens has released updates for several affected products and recommends to update to the latest versions. Siemens recommends specific countermeasures for products where updates are not available.
WID-SEC-W-2023-1986NAME:WRECK: Mehrere Schwachstellen in TCP/IP StacksDeutsch2021-04-15csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Siemens Nucleus Net, Siemens Nucleus RTOS, Microsoft Azure RTOS NetX und Wind River VxWorks ausnutzen, um beliebigen Programmcode mit Administratorrechten auszuführen oder einen Denial of Service zu verursachen.
ICSA-21-103-14Siemens Nucleus DNS (Update A)2021-04-13icsa · cisa_csaf_otUS
Security researchers discovered and disclosed 9 vulnerabilities in several DNS implementations, also known as “NAME:WRECK” vulnerabilities. The vulnerability described in this advisory is from this set. The DNS client of of the networking component (Nucleus NET) in Nucleus Real-Time Operating System (RTOS) contains a vulnerability related to the handling of UDP port numbers in DNS requests that could allow an attacker to poison the DNS cache or spoof DNS resolving. Siemens has released updates for several affected products and recommends to update to the latest versions. Siemens recommends specific countermeasures for products where updates are not available.

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd cert_bund cisa_csaf_ot nvd siemens_psirt NVD CVE.org MITRE

published 2021-04-22modified 2026-06-17

references (7)

External citations — patches, advisories, analysis.

scry

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