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Vulnerabilities

Vulnerability · CVE-2026-72923

Microsoft.OpenApi.YamlReader vulnerable to denial of service via YAML alias expansion

Published Sep 8, 2026 · catalog updated Oct 14, 2026 · OpenAPI.NET

Check if you run it

No confirmed exploitation is on record for CVE-2026-72923. EPSS is 1.90%. Act only if a listed version of OpenAPI.NET is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.90%
Remediation
Version ranges on file
Affected products
NuGet Microsoft.OpenApi.Readers · NuGet Microsoft.OpenApi.YamlReader · nuget Microsoft.OpenApi.Readers · nuget Microsoft.OpenApi.YamlReader · nuget microsoft.openapi.readers · nuget microsoft.openapi.yamlreader

### Impact A small YAML OpenAPI document containing nested anchors and aliases can cause uncontrolled resource consumption in Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers. The issue affects OpenAPI document parsing through the public YAML reader APIs and can cause the parsing process to allocate excessive memory and terminate through out-of-memory conditions. ## Affected versions ### Microsoft.OpenApi.YamlReader * * ### Microsoft.OpenApi.Readers * ### Patches * For the 1.X major version, versions 1.6.30 and above are patched. * For the 2.X major version, versions 2.12.0 and above are patched. * For the 3.X major version, versions 3.10.0 and above are patched. ## Impact Applications, CLIs, developer tools, or services that parse untrusted YAML OpenAPI documents in-process may be terminated by a crafted YAML document containing nested anchors and aliases. 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 Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers parses YAML through SharpYaml. SharpYaml represents aliases as shared instances in a directed acyclic graph, so the initial parsed YAML graph remains small. During conversion to , aliases must be materialized as independent nodes because instances cannot be attached to multiple parents. Without a bound on that conversion work, a small YAML document using nested anchors and aliases can expand exponentially during conversion. With nested anchors each referenced times, conversion can require materialized JSON nodes, leading to excessive memory allocation and possible process termination. This is an uncontrolled resource consumption vulnerability, also known as a "billion laughs" style denial of service. ### Example payload ## Remediation Users should upgrade to Microsoft.OpenApi.YamlReader or , or Microsoft.OpenApi.Reader

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • NuGet Microsoft.OpenApi.Readers0 → 1.6.30
  • NuGet Microsoft.OpenApi.YamlReader2.0.0-preview.11 → 2.12.0
  • NuGet Microsoft.OpenApi.YamlReader3.0.0 → 3.10.0
  • nuget Microsoft.OpenApi.Readers< 1.6.30
  • nuget Microsoft.OpenApi.YamlReader>= 2.0.0-preview.11, < 2.12.0
  • nuget Microsoft.OpenApi.YamlReader>= 3.0.0, < 3.10.0
  • nuget microsoft.openapi.readersversion unspecified
  • nuget microsoft.openapi.yamlreaderversion unspecified
  • vendor microsoft OpenAPI.NETversion unspecified

How to fix CVE-2026-72923

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-72923. EPSS is 1.90%. Act only if a listed version of OpenAPI.NET is installed.

Which versions are affected?

Compare what you have installed with Microsoft.OpenApi.Readers 0 → 1.6.30; Microsoft.OpenApi.YamlReader 2.0.0-preview.11 → 2.12.0; Microsoft.OpenApi.YamlReader 3.0.0 → 3.10.0; Microsoft.OpenApi.Readers < 1.6.30. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-400: Uncontrolled Resource Consumption; CWE-770: Allocation of Resources Without Limits or Throttling. EPSS 1.90%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 14, 2026 · GitHub Advisory Database

    Detected

    ### Impact A small YAML OpenAPI document containing nested anchors and aliases can cause uncontrolled resource consumption in Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers. The issue affects OpenAPI document parsing through the public YAML reader APIs and can cause the parsing process to allocate excessive memory and terminate through out-of-memory conditions. ## Affected versions ###

  2. Oct 14, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.OpenApi.YamlReader fixed in 3.10.0; Microsoft.OpenApi.YamlReader fixed in 2.12.0; Microsoft.OpenApi.Readers fixed in 1.6.30

  3. Oct 14, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.OpenApi.YamlReader fixed in 3.10.0

  4. Oct 14, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.OpenApi.YamlReader fixed in 2.12.0

  5. Oct 14, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.OpenApi.Readers fixed in 1.6.30

  6. Oct 14, 2026 · GitHub Advisory Database

    Updated

    ### Impact A small YAML OpenAPI document containing nested anchors and aliases can cause uncontrolled resource consumption in Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers. The issue affects OpenAPI document parsing through the public YAML reader APIs and can cause the parsing process to allocate excessive memory and terminate through out-of-memory conditions. ## Affected versions ###

  7. Oct 14, 2026 · NIST NVD

    Updated

    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. In Microsoft.OpenApi.Readers versions before 1.6.30 and Microsoft.OpenApi.YamlReader from 2.0.0-preview.11 through 2.11.0 and 3.0.0 through 3.9.0, parsing a YAML OpenAPI document with nested anchors and aliases can consume unc

Sources

  • CVE.orgVulnerability recordCVE-2026-72923

    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. In Microsoft.OpenApi.Readers versions before 1.6.30 and Microsoft.OpenApi.YamlReader from 2.0.0-preview.11

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-72923

    30-day exploitation probability 1.9%

    first.org
  • GitHub Advisory DatabasePackage advisoryGHSA-7pxr-59rr-hqj2

    GitHub Advisory Database record mirrored by OSV.

    github.com
  • GitLab Advisory DatabasePackage advisoryCVE-2026-72923

    A small YAML OpenAPI document containing nested anchors and aliases can cause uncontrolled resource consumption in Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers. The issue affects OpenAPI document parsing through the public YAML reader APIs and can cause the parsing process to allocate excessive memory and terminate through out-of-memory conditions. Applications, CLIs, developer tools

    advisories.gitlab.com
  • NIST NVDVulnerability recordCVE-2026-72923

    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. In Microsoft.OpenApi.Readers versions before 1.6.30 and Microsoft.OpenApi.YamlReader from 2.0.0-preview.11

    nvd.nist.gov
  • OpenSSF OSV / OSV ScannerPackage advisoryGHSA-7pxr-59rr-hqj2

    Microsoft.OpenApi.YamlReader vulnerable to denial of service via YAML alias expansion

    osv.dev

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.