# CVE-2021-27432: Denial of service in OPC Foundation OPC UA .NET Standard and OPC UA .NET Legacy

> An attacker can trigger a stack overflow via uncontrolled recursion in the OPC UA .NET library, causing a denial of service.

- **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 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-5rm8-9376-7gg5

## What is CVE-2021-27432?

CVE-2021-27432 is a high-severity denial of service vulnerability in OPC Foundation OPC UA .NET Standard and OPC UA .NET Legacy, published on 20 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OPC Foundation UA .NET Standard versions prior to 1.4.365.48 and OPC UA .NET Legacy are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2021-27432?

It affects 2 products.


Products: Opcfoundation Ua-.Net-Legacy, Opcfoundation Ua .Net Standard Stack.

## How do I fix CVE-2021-27432?

No fix has been published for CVE-2021-27432 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27432 being exploited?

There is no known exploitation of CVE-2021-27432 in the wild and no public exploit code.

## Other vulnerabilities in OPC Foundation OPC UA .NET Standard and OPC UA .NET Legacy

- [CVE-2017-12070](https://insights.sbomify.com/CVE-2017-12070/): Supply chain in n/a (high 8.8)
- [CVE-2018-12585](https://insights.sbomify.com/CVE-2018-12585/): XML external entity in n/a (high 8.2)
- [CVE-2018-12087](https://insights.sbomify.com/CVE-2018-12087/): Moderate severity vulnerability that affects OPCFoundation.NetStandard.Opc.Ua (medium 5.3)
- [CVE-2018-7559](https://insights.sbomify.com/CVE-2018-7559/): OPC UA applications can allow a remote attacker to determine a Server's private key (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27432 and fix it if it is affected.

What it is: CVE-2021-27432 is a high-severity denial of service vulnerability in OPC Foundation OPC UA .NET Standard and OPC UA .NET Legacy, published on 20 May 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-2021-27432 in the wild and no public exploit code.

Affected product: OPC Foundation OPC UA .NET Standard and OPC UA .NET Legacy. 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-2021-27432/ (Markdown: https://insights.sbomify.com/CVE-2021-27432/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27432
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27432
- OSV: https://osv.dev/vulnerability/CVE-2021-27432

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-27432/
Summaries are generated and may contain mistakes; the official description above is the record.