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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-49451?
4 open source packages ship an affected version, including Microsoft.OpenApi.
| Package | 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-49451 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-49451 exists.
Sources
Also known as GHSA-v5pm-xwqc-g5wc.