# CVE-2021-31881: Denial of service in Capital Embedded AR Classic 431-422

> A missing length validation in the DHCP client allows attackers to cause a Denial-of-Service condition in Siemens Capital Embedded AR Classic devices.

- **Severity:** High 7.1 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Nov 2021
- **Updated:** 11 Mar 2025
- **Also known as:** GHSA-x327-px9p-wgr2

## What is CVE-2021-31881?

CVE-2021-31881 is a high-severity denial of service vulnerability in Siemens Capital Embedded AR Classic 431-422, published on 9 Nov 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability has been identified in Capital Embedded AR Classic 431-422 (All versions), Capital Embedded AR Classic R20-11 (All versions < V2303). When processing a DHCP OFFER message, the DHCP client application does not validate the length of the Vendor option(s), leading to Denial-of-Service conditions. (FSMD-2021-0008)

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-31881?

It affects 10 products.


Products: Siemens Apogee Modular Building Controller Firmware, Siemens Apogee Modular Equiment Controller Firmware, Siemens Apogee Pxc Compact Firmware, Siemens Apogee Pxc Modular Firmware, Siemens Capital Vstar, Siemens Nucleus Net, Siemens Nucleus Readystart V3, Siemens Nucleus Source Code, Siemens Talon Tc Compact Firmware, Siemens Talon Tc Modular Firmware.

## How do I fix CVE-2021-31881?

No fix has been published for CVE-2021-31881 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-31881 being exploited?

There is no known exploitation of CVE-2021-31881 in the wild and no public exploit code.

## Other vulnerabilities in Siemens Capital Embedded AR Classic 431-422

- [CVE-2021-31884](https://insights.sbomify.com/CVE-2021-31884/): Memory corruption in APOGEE MBC (PPC) (BACnet) (critical 9.8)
- [CVE-2021-31886](https://insights.sbomify.com/CVE-2021-31886/): Memory corruption in APOGEE MBC (PPC) (BACnet) (critical 9.8)
- [CVE-2021-31887](https://insights.sbomify.com/CVE-2021-31887/): Memory corruption in APOGEE MBC (PPC) (BACnet) (high 8.8)
- [CVE-2021-31888](https://insights.sbomify.com/CVE-2021-31888/): Memory corruption in APOGEE MBC (PPC) (BACnet) (high 8.8)
- [CVE-2022-38371](https://insights.sbomify.com/CVE-2022-38371/): Denial of service in APOGEE MBC (PPC) (BACnet) (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31881 and fix it if it is affected.

What it is: CVE-2021-31881 is a high-severity denial of service vulnerability in Siemens Capital Embedded AR Classic 431-422, published on 9 Nov 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-31881 in the wild and no public exploit code.

Affected product: Siemens Capital Embedded AR Classic 431-422. 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-2021-31881/ (Markdown: https://insights.sbomify.com/CVE-2021-31881/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31881
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31881
- OSV: https://osv.dev/vulnerability/CVE-2021-31881

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31881/
Summaries are generated and may contain mistakes; the official description above is the record.