ICSA-21-103-14: Siemens Nucleus DNS (Update A)
CISA advisory · released 2021-04-13
Source record Collected from CISA's CSAF advisory feed
- Distribution label in the document: TLP:WHITE
- Revision 4, 2025-05-06 (final)
CISA's summary
Summary: 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.
Products, as the advisory lists them
| Vendor | Product | Version |
|---|---|---|
| Siemens | Nucleus NET | vers:all/* |
| Siemens | Nucleus ReadyStart V3 | <V2013.08 |
| Siemens | Nucleus Source Code | including_affected_DNS_modules |
DeSpy has not checked any unit, hardware revision or firmware.
Vulnerabilities in this advisory
- CVE-2021-27393 — CVE-2021-27393 · CWE-330
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.
Acknowledgments, as the advisory lists them
- Siemens ProductCERT: reporting this vulnerability to CISA.
- Daniel dos Santos, Forescout Technologies Inc.: coordinated disclosure
The advisory's legal notice
Siemens Security Advisories are subject to the terms and conditions contained in Siemens' underlying license terms or other applicable agreements previously agreed to with Siemens (hereinafter "License Terms"). To the extent applicable to information, software or documentation made available in or through a Siemens Security Advisory, the Terms of Use of Siemens' Global Website (https://www.siemens.com/terms_of_use, hereinafter "Terms of Use"), in particular Sections 8-10 of the Terms of Use, shall apply additionally. In case of conflicts, the License Terms shall prevail over the Terms of Use.
Sources
DeSpy's copy of this version is dated 2026-09-28.
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