# CVE-2026-49451: Microsoft.OpenAPI: Circular schema references may terminate OpenAPI parsing

> Attackers can cause application crashes via stack overflow by submitting OpenAPI documents with circular schema references to the Microsoft.OpenApi library.

- **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:** Yes
- **Published:** 30 Jun 2026
- **Updated:** 30 Jun 2026
- **Also known as:** GHSA-v5pm-xwqc-g5wc

## What is CVE-2026-49451?

CVE-2026-49451 is a high-severity denial of service vulnerability in microsoft OpenAPI.NET, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The OpenAPI.NET SDK contains a useful object model for OpenAPI documents in .NET along with common serializers to extract raw OpenAPI JSON and YAML documents from the model. From 2.0.0-preview11 until 2.7.5 and 3.5.4, a small OpenAPI document containing a circular schema reference can cause process termination through stack overflow in Microsoft.OpenApi. The issue affects OpenAPI document parsing through public OpenAPI.NET reader APIs and has been confirmed across both JSON and YAML reader paths. This vulnerability is fixed in 2.7.5 and 3.5.4.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-49451?

4 open source packages ship an affected version, including Microsoft.OpenApi.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `Microsoft.OpenApi` | NuGet | From 2.0.0-preview.11 | 2.7.5 |
| `Microsoft.OpenApi` | NuGet | From 2.0.0-preview.11 | 2.7.5 |
| `Microsoft.OpenApi` | NuGet | From 3.0.0 | 3.5.4 |
| `Microsoft.OpenApi` | NuGet | From 3.0.0 | 3.5.4 |

## How do I fix CVE-2026-49451?

Upgrade Microsoft.OpenApi to a fixed version for your release line: 2.7.5 or 3.5.4.

## Is CVE-2026-49451 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49451 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49451 and fix it if it is affected.

What it is: CVE-2026-49451 is a high-severity denial of service vulnerability in microsoft OpenAPI.NET, published on 30 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49451 exists.

Affected packages and fixed versions:
- Microsoft.OpenApi (NuGet): affected from 2.0.0-preview.11; fixed in 2.7.5
- Microsoft.OpenApi (NuGet): affected from 2.0.0-preview.11; fixed in 2.7.5
- Microsoft.OpenApi (NuGet): affected from 3.0.0; fixed in 3.5.4
- Microsoft.OpenApi (NuGet): affected from 3.0.0; fixed in 3.5.4

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-2026-49451/ (Markdown: https://insights.sbomify.com/CVE-2026-49451/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49451
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49451
- OSV: https://osv.dev/vulnerability/CVE-2026-49451

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49451/
Summaries are generated and may contain mistakes; the official description above is the record.