CVE-2026-49451 is a high-severity security vulnerability in Microsoft.OpenAPI (nuget), affecting versions >= 2.0.0-preview11, <= 2.7.4. It is fixed in 2.7.5, 3.5.4.
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-preview11, <= 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 <file> workflow. That workflow parses OpenAPI files in-process using Microsoft.OpenApi and Microsoft.OpenApi.YamlReader. Example payload Remediation Users should upgrade to Microsoft.OpenApi 2.7.5 or 3.5.4, depending on the major version line they consume. Applications that parse OpenAPI documents from untrusted sources should avoid parsing those documents in the primary application process when possible. Running parsing in an isolated process can reduce the blast radius of parser failures.
CVE-2026-49451 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (2.7.5, 3.5.4). Upgrading removes the vulnerable code path.
nuget
Microsoft.OpenAPI (>= 2.0.0-preview11, <= 2.7.4)Microsoft.OpenAPI (>= 3.0.0, <= 3.5.3)Microsoft.OpenAPI → 2.7.5 (nuget)Microsoft.OpenAPI → 3.5.4 (nuget)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Already deployed Kodem? See CVE-2026-49451 in your environment →Upgrade the following packages to resolve this vulnerability:
Microsoft.OpenAPI to 2.7.5 or laterMicrosoft.OpenAPI to 3.5.4 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-49451 is a high-severity security vulnerability in Microsoft.OpenAPI (nuget), affecting versions >= 2.0.0-preview11, <= 2.7.4. It is fixed in 2.7.5, 3.5.4.
CVE-2026-49451 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
Microsoft.OpenAPI (nuget) versions >= 2.0.0-preview11, <= 2.7.4 is affected.
Yes. CVE-2026-49451 is fixed in 2.7.5, 3.5.4. Upgrade to this version or later.
Whether CVE-2026-49451 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Microsoft.OpenAPI to 2.7.5 or laterMicrosoft.OpenAPI to 3.5.4 or later