Microsoft.OpenAPI: Circular schema references may terminate OpenAPI parsing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-49451: 0.75% estimated exploitation activity in the next 30 days; percentile 54.88 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. Affected versions - = 2.0.0-preview.11, <= 2.7.4 - = 3.0.0, <= 3.5.3 Patches - For the 2.X major version, versions 2.7.5 and above are patched. - For the 3.X major version, versions 3.5.4 and above are patched. - For the 1.X major version, the issue does not apply since that version of the library could not resolve references that pointed to another reference. Impact Applications, CLIs, developer tools, or services that parse untrusted OpenAPI documents in-process may be terminated by a crafted OpenAPI document containing circular schema references. The impact is availability/process termination only. This report does not claim remote code execution, authentication bypass, credential exposure,…

Published by the source

30 Jun 2026, 15:56 UTC

Last modified by the source

6 Jul 2026, 12:57 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v5pm-xwqc-g5wc

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# Patch Next advisory brief: CVE-2026-49451

Advisory: Microsoft.OpenAPI: Circular schema references may terminate OpenAPI parsing
IDs: CVE-2026-49451, GHSA-v5pm-xwqc-g5wc
Record: https://patchnext.com/advisories/cve-2026-49451 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.openapi 3.5.4, 2.7.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.openapi: affected >= 3.0.0, <= 3.5.3; >= 2.0.0-preview.11, <= 2.7.4; fixed in 3.5.4, 2.7.5

## Suggested inspection (read-only)
- NuGet microsoft.openapi: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on microsoft.openapi.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v5pm-xwqc-g5wc (GitHub-reviewed advisory GHSA-v5pm-xwqc-g5wc lists affected ranges: NuGet microsoft.openapi >=3.0.0 =2.0.0-preview.11 <=2.7.4)

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