# CVE-2021-27391: Memory corruption in APOGEE MBC (PPC) (P2 Ethernet)

> Unauthenticated remote attackers can execute arbitrary code with root privileges via a buffer overflow in the web server's Host parameter parsing.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2021
- **Updated:** 23 Apr 2025
- **Also known as:** GHSA-98pm-v23p-r2wf

## What is CVE-2021-27391?

CVE-2021-27391 is a critical memory corruption vulnerability in Siemens APOGEE MBC (PPC) (P2 Ethernet), published on 14 Sep 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 APOGEE MBC (PPC) (P2 Ethernet) (All versions >= V2.6.3), APOGEE MEC (PPC) (P2 Ethernet) (All versions >= V2.6.3), APOGEE PXC Compact (BACnet) (All versions < V3.5.3), APOGEE PXC Compact (P2 Ethernet) (All versions >= V2.8), APOGEE PXC Modular (BACnet) (All versions < V3.5.3), APOGEE PXC Modular (P2 Ethernet) (All versions >= V2.8), TALON TC Compact (BACnet) (All versions < V3.5.3), TALON TC Modular (BACnet) (All versions < V3.5.3). The web server of affected devices lacks proper bounds checking when parsing the Host parameter in HTTP requests, which could lead to a buffer overflow. An unauthenticated remote attacker could exploit this vulnerability to execute arbitrary code on the device with root privileges.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2021-27391?

It affects 8 products.


Products: Siemens Apogee Mbc \(Ppc\) \(P2 Ethernet\) Firmware, Siemens Apogee Mec \(Ppc\) \(P2 Ethernet\) Firmware, Siemens Apogee Pxc Bacnet Automation Controller Firmware, Siemens Apogee Pxc Compact \(P2 Ethernet\) Firmware, Siemens Apogee Pxc Modular \(Bacnet\) Firmware, Siemens Apogee Pxc Modular \(P2 Ethernet\) Firmware, Siemens Talon Tc Compact \(Bacnet\) Firmware, Siemens Talon Tc Modular \(Bacnet\) Firmware.

## How do I fix CVE-2021-27391?

No fix has been published for CVE-2021-27391 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27391 being exploited?

There is no known exploitation of CVE-2021-27391 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27391 and fix it if it is affected.

What it is: CVE-2021-27391 is a critical memory corruption vulnerability in Siemens APOGEE MBC (PPC) (P2 Ethernet), published on 14 Sep 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-2021-27391 in the wild and no public exploit code.

Affected product: Siemens APOGEE MBC (PPC) (P2 Ethernet). 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-2021-27391/ (Markdown: https://insights.sbomify.com/CVE-2021-27391/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27391
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27391
- OSV: https://osv.dev/vulnerability/CVE-2021-27391

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-27391/
Summaries are generated and may contain mistakes; the official description above is the record.