Vulnerability in Microsoft.OpenAPI (CVE-2026-49451)
Summary
Vulnerability in Microsoft.OpenAPI (CVE-2026-49451). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 3.5.4 or later.
Original description
The description as published by the source.
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, privilege escalation, data exposure, or Microsoft hosted service impact.
Details
A standalone isolated-process harness confirmed repeatable process termination through public OpenAPI.NET reader APIs. The issue reproduces in the affected released NuGet packages and affects both JSON and YAML reader paths.
A separate Microsoft-owned local consumer, microsoft/kiota, also reproduces the termination through the kiota show --openapi workflow. That workflow parses Ope…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-49451 has been found in Microsoft.OpenAPI.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade Microsoft.OpenAPI to 3.5.4 or later.
If unsure, ask your IT team or search "Microsoft.OpenAPI CVE-2026-49451" on the vendor's site.
CVE-2026-49451 (Microsoft.OpenAPI) — CWE-674 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 3.5.4 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-674) exists in Microsoft.OpenAPI.
Check the vendor advisory for the affected versions of Microsoft.OpenAPI.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.5.4.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Microsoft.OpenAPI' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'Microsoft.OpenAPI' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
Microsoft.OpenAPIを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade Microsoft.OpenAPI to 3.5.4ステージング環境で 3.5.4 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com