CVE-2021-27393

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-04-22 · updated 2026-06-17
Weakness: CWE-330

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.

Affected products

Siemens Nucleus NET: all versions
Siemens Nucleus ReadyStart V3: before 2013.08 — fixed in 2013.08
Siemens Nucleus Source Code: all versions

How to fix

Upgrade to a fixed version: Siemens Nucleus ReadyStart V3 2013.08. Check the vendor advisory for mitigations.

References

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