# CVE-2021-37740: Denial of service in n/a

> Remote attackers can cause denial of service on MDT KNXnet/IP Secure devices by sending a malformed SESSION_REQUEST frame, requiring a reboot to recover.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 20 Apr 2022
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-fgcc-2fx7-p23v

## What is CVE-2021-37740?

CVE-2021-37740 is a high-severity denial of service vulnerability in n/a, published on 20 Apr 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A denial of service vulnerability exists in MDT's firmware for the KNXnet/IP Secure router SCN-IP100.03 and KNX IP interface SCN-IP000.03 before v3.0.4, that allows a remote attacker to turn the device unresponsive to all requests on the KNXnet/IP Secure layer, until the device is rebooted, via a SESSION_REQUEST frame with a modified total length field.

## Which versions are affected by CVE-2021-37740?

It affects 2 products.


Products: Mdt Scn-Ip000.03 Firmware, Mdt Scn-Ip100.03 Firmware.

## How do I fix CVE-2021-37740?

No fix has been published for CVE-2021-37740 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-37740 being exploited?

There is no known exploitation of CVE-2021-37740 in the wild and no public exploit code.

Public exploit code:

- PoC for DoS vulnerability CVE-2021-37740 in firmware v3.0.3 of SCN-IP100.03 and SCN-IP000.03 by MDT. The bug has been fixed in firmware v3.0.4. (github_poc): https://github.com/robertguetzkow/CVE-2021-37740

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-37740 and fix it if it is affected.

What it is: CVE-2021-37740 is a high-severity denial of service vulnerability in n/a, published on 20 Apr 2022. 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-2021-37740 in the wild and no public exploit code.

Affected product: n/a. 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-2021-37740/ (Markdown: https://insights.sbomify.com/CVE-2021-37740/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-37740
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-37740
- OSV: https://osv.dev/vulnerability/CVE-2021-37740

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-37740/
Summaries are generated and may contain mistakes; the official description above is the record.