# CVE-2023-27321: OPC Foundation UA .NET Standard ConditionRefresh Resource Exhaustion Denial-of-Service Vulnerability

> Remote attackers can cause denial of service in OPC Foundation UA .NET Standard by exhausting server resources via ConditionRefresh requests.

- **Severity:** High 7.5 (`CVSS:3.0/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:** Yes
- **Published:** 7 May 2024
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-vpf7-r2fv-75m9

## What is CVE-2023-27321?

CVE-2023-27321 is a high-severity denial of service vulnerability in OPC Foundation UA .NET Standard, published on 7 May 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OPC Foundation UA .NET Standard ConditionRefresh Resource Exhaustion Denial-of-Service Vulnerability. This vulnerability allows remote attackers to create a denial-of-service condition on affected installations of OPC Foundation UA .NET Standard. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the handling of OPC UA ConditionRefresh requests. By sending a large number of requests, an attacker can consume all available resources on the server. An attacker can leverage this vulnerability to create a denial-of-service condition on the system. Was ZDI-CAN-20505.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2023-27321?

2 open source packages ship an affected version, including OPCFoundation.NetStandard.Opc.Ua.Server. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `OPCFoundation.NetStandard.Opc.Ua.Server` | NuGet | All versions | 1.4.371.86 |
| `OPCFoundation.NetStandard.Opc.Ua.Server` | NuGet | All versions | 1.4.371.86 |

Products: Opcfoundation Ua-.Netstandard.

## How do I fix CVE-2023-27321?

Upgrade OPCFoundation.NetStandard.Opc.Ua.Server to 1.4.371.86 or later.

## Is CVE-2023-27321 being exploited?

There is no known exploitation of CVE-2023-27321 in the wild and no public exploit code.

## Other vulnerabilities in OPC Foundation UA .NET Standard

- [CVE-2023-31048](https://insights.sbomify.com/CVE-2023-31048/): Exposure of Sensitive Information in OPC UA .NET Standard Reference Server (medium 5.3)
- [CVE-2020-29457](https://insights.sbomify.com/CVE-2020-29457/): Improper Certificate Validation in OPCFoundation.NetStandard.Opc.Ua.Core (medium 4.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-27321 and fix it if it is affected.

What it is: CVE-2023-27321 is a high-severity denial of service vulnerability in OPC Foundation UA .NET Standard, published on 7 May 2024. 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-2023-27321 in the wild and no public exploit code.

Affected packages and fixed versions:
- OPCFoundation.NetStandard.Opc.Ua.Server (NuGet): affected all versions; fixed in 1.4.371.86
- OPCFoundation.NetStandard.Opc.Ua.Server (NuGet): affected all versions; fixed in 1.4.371.86

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-2023-27321/ (Markdown: https://insights.sbomify.com/CVE-2023-27321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-27321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-27321
- OSV: https://osv.dev/vulnerability/CVE-2023-27321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-27321/
Summaries are generated and may contain mistakes; the official description above is the record.