# CVE-2021-27393: Other in Nucleus NET

> Insufficient UDP port randomization in the DNS client allows attackers to poison DNS cache or spoof DNS resolution.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Apr 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-x7x4-r59j-h6w9

## What is CVE-2021-27393?

CVE-2021-27393 is a medium-severity vulnerability in Siemens Nucleus NET, published on 22 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-330 (Use of Insufficiently Random Values)

## Which versions are affected by CVE-2021-27393?

It affects 3 products.


Products: Siemens Nucleus Net, Siemens Nucleus Readystart V3, Siemens Nucleus Source Code.

## How do I fix CVE-2021-27393?

No fix has been published for CVE-2021-27393 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27393 being exploited?

There is no known exploitation of CVE-2021-27393 in the wild and no public exploit code.

## Other vulnerabilities in Siemens Nucleus NET

- [CVE-2020-15795](https://insights.sbomify.com/CVE-2020-15795/): Memory corruption in APOGEE PXC Compact (BACnet) (high 8.1)
- [CVE-2020-27009](https://insights.sbomify.com/CVE-2020-27009/): Memory corruption in APOGEE PXC Compact (BACnet) (high 8.1)
- [CVE-2020-27736](https://insights.sbomify.com/CVE-2020-27736/): Memory corruption in APOGEE PXC Compact (BACnet) (medium 6.5)
- [CVE-2020-27737](https://insights.sbomify.com/CVE-2020-27737/): Memory corruption in APOGEE PXC Compact (BACnet) (medium 6.5)
- [CVE-2020-27738](https://insights.sbomify.com/CVE-2020-27738/): Memory corruption in APOGEE PXC Compact (BACnet) (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27393 and fix it if it is affected.

What it is: CVE-2021-27393 is a medium-severity vulnerability in Siemens Nucleus NET, published on 22 Apr 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-27393 in the wild and no public exploit code.

Affected product: Siemens Nucleus NET. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-27393/ (Markdown: https://insights.sbomify.com/CVE-2021-27393/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27393
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27393
- OSV: https://osv.dev/vulnerability/CVE-2021-27393

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27393/
Summaries are generated and may contain mistakes; the official description above is the record.