# CVE-2019-5636: Beckhoff TwinCAT Discovery Service Denial of Service

> A malformed UDP packet causes the ADS Discovery Service to shut down in Beckhoff TwinCAT Runtime, disrupting discovery services without stopping device operations.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Nov 2019
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-pv38-9q3c-3qq8

## What is CVE-2019-5636?

CVE-2019-5636 is a medium-severity denial of service vulnerability in Beckhoff TwinCAT 2, published on 21 Nov 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When a Beckhoff TwinCAT Runtime receives a malformed UDP packet, the ADS Discovery Service shuts down. Note that the TwinCAT devices are still performing as normal. This issue affects TwinCAT 2 version 2304 (and prior) and TwinCAT 3.1 version 4204.0 (and prior).

Weakness: CWE-404 (Improper Resource Shutdown or Release)

## Which versions are affected by CVE-2019-5636?

It affects 1 product.


Products: Beckhoff Twincat.

## How do I fix CVE-2019-5636?

No fix has been published for CVE-2019-5636 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-5636 being exploited?

There is no known exploitation of CVE-2019-5636 in the wild and no public exploit code.

## Other vulnerabilities in Beckhoff TwinCAT 2

- [CVE-2019-16871](https://insights.sbomify.com/CVE-2019-16871/): Auth bypass in n/a (critical 9.8)
- [CVE-2017-16726](https://insights.sbomify.com/CVE-2017-16726/): Weak cryptography in Beckhoff TwinCAT (critical 9.1)
- [CVE-2018-7502](https://insights.sbomify.com/CVE-2018-7502/): Privilege escalation in Beckhoff TwinCAT PLC products (high 7.8)
- [CVE-2019-5637](https://insights.sbomify.com/CVE-2019-5637/): Beckhoff TwinCAT Profinet Driver Divide-by-Zero Denial of Service (high 7.5)
- [CVE-2017-16718](https://insights.sbomify.com/CVE-2017-16718/): Weak cryptography in Beckhoff TwinCAT (medium 5.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-5636 and fix it if it is affected.

What it is: CVE-2019-5636 is a medium-severity denial of service vulnerability in Beckhoff TwinCAT 2, published on 21 Nov 2019. 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-2019-5636 in the wild and no public exploit code.

Affected product: Beckhoff TwinCAT 2. 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-2019-5636/ (Markdown: https://insights.sbomify.com/CVE-2019-5636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-5636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-5636
- OSV: https://osv.dev/vulnerability/CVE-2019-5636

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-5636/
Summaries are generated and may contain mistakes; the official description above is the record.