Vulnerability-Lookup

CVE-2026-72923 (GCVE-0-2026-72923)

Vulnerability from cvelistv5 – Published: 2026-09-08 17:12 – Updated: 2026-10-14 20:08

Title

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

Summary

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 uncontrolled memory. SharpYaml represents aliases as shared nodes in a small directed acyclic graph, but conversion to independent OpenAPI or System.Text.Json.Nodes.JsonNode trees duplicates every aliased path; without a node-count or nesting-depth limit, N nested anchors referenced k times can require k^N materialized nodes and terminate the process through an out-of-memory condition. The fixed readers bound materialization to 5,000,000 nodes and a nesting depth of 64 by default and report an OpenApiDiagnostic error when a limit is exceeded. This vulnerability is fixed in Microsoft.OpenApi.Readers 1.6.30 and Microsoft.OpenApi.YamlReader 2.12.0 and 3.10.0.

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-08 17:36 UTC

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7887 records in the last 180 days details

References

4 references

URL	Tags
https://github.com/microsoft/OpenAPI.NET/security…	x_refsource_CONFIRM
https://github.com/microsoft/OpenAPI.NET/commit/1…	x_refsource_MISC
https://github.com/microsoft/OpenAPI.NET/commit/2…	x_refsource_MISC
https://github.com/microsoft/OpenAPI.NET/commit/4…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
microsoft	OpenAPI.NET	Affected: >= 3.0.0, < 3.10.0 Affected: >= 2.0.0-preview.11, < 2.12.0 Affected: < 1.6.30	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-72923

Vulnerability from fkie_nvd - Published: 2026-09-08 18:20 - Updated: 2026-10-14 21:17

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/microsoft/OpenAPI.NET/commit/1f9aea9bdcbf4066b59ce33b3bd8f97ed9cb4766
	security-advisories@github.com	https://github.com/microsoft/OpenAPI.NET/commit/21793261d6860fb6e607b71fd95c0bd320724764
	security-advisories@github.com	https://github.com/microsoft/OpenAPI.NET/commit/4db9af07d112cdf45170b7a946f956ffe74fa14e
	security-advisories@github.com	https://github.com/microsoft/OpenAPI.NET/security/advisories/GHSA-7pxr-59rr-hqj2

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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  ],
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GHSA-7PXR-59RR-HQJ2

Vulnerability from github – Published: 2026-10-14 20:11 – Updated: 2026-10-14 20:11

Summary

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

Details

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

>= 2.0.0-preview.11, < 2.12.0
>= 3.0.0, < 3.10.0

Microsoft.OpenApi.Readers

< 1.6.30

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 YamlNode instances in a directed acyclic graph, so the initial parsed YAML graph remains small. During conversion to System.Text.Json.Nodes.JsonNode, aliases must be materialized as independent nodes because JsonNode 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 N nested anchors each referenced k times, conversion can require k^N 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

openapi: 3.0.0
info:
  title: Test
  version: 0.0.1
paths: {}
x-a: &a ["lol", "lol", "lol", "lol", "lol", "lol", "lol", "lol", "lol"]
x-b: &b [*a, *a, *a, *a, *a, *a, *a, *a, *a]
x-c: &c [*b, *b, *b, *b, *b, *b, *b, *b, *b]
x-d: &d [*c, *c, *c, *c, *c, *c, *c, *c, *c]
x-e: &e [*d, *d, *d, *d, *d, *d, *d, *d, *d]
x-f: &f [*e, *e, *e, *e, *e, *e, *e, *e, *e]

Remediation

Users should upgrade to Microsoft.OpenApi.YamlReader 2.12.0 or 3.10.0, or Microsoft.OpenApi.Readers 1.6.30, depending on the major version line they consume.

The patched versions bound YAML-to-JSON conversion work and fail fast instead of allowing unbounded expansion. The default limits are:

Maximum materialized node count: 5,000,000
Maximum nesting depth: 64

When the limits are exceeded, OpenApiYamlReader.Read reports an OpenApiDiagnostic error and does not return a parsed document.

The limits are exposed as process-wide static properties on YamlConverter for consumers that need to tune them for trusted workloads:

YamlConverter.MaxNodeCount
YamlConverter.MaxDepth

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.

Severity

7.5 (High)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "Microsoft.OpenApi.YamlReader"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "Microsoft.OpenApi.YamlReader"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0-preview.11"
            },
            {
              "fixed": "2.12.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "Microsoft.OpenApi.Readers"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.30"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-72923"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400",
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-14T20:11:29Z",
    "nvd_published_at": "2026-09-08T18:20:16Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nA 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.\n\n## Affected versions\n\n### Microsoft.OpenApi.YamlReader\n\n* `\u003e= 2.0.0-preview.11, \u003c 2.12.0`\n* `\u003e= 3.0.0, \u003c 3.10.0`\n\n### Microsoft.OpenApi.Readers\n\n* `\u003c 1.6.30`\n\n### Patches\n\n* For the 1.X major version, versions 1.6.30 and above are patched.\n* For the 2.X major version, versions 2.12.0 and above are patched.\n* For the 3.X major version, versions 3.10.0 and above are patched.\n\n## Impact\n\nApplications, 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.\n\nThe 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.\n\n## Details\n\nMicrosoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers parses YAML through SharpYaml. SharpYaml represents aliases as shared `YamlNode` instances in a directed acyclic graph, so the initial parsed YAML graph remains small. During conversion to `System.Text.Json.Nodes.JsonNode`, aliases must be materialized as independent nodes because `JsonNode` instances cannot be attached to multiple parents.\n\nWithout a bound on that conversion work, a small YAML document using nested anchors and aliases can expand exponentially during conversion. With `N` nested anchors each referenced `k` times, conversion can require `k^N` materialized JSON nodes, leading to excessive memory allocation and possible process termination.\n\nThis is an uncontrolled resource consumption vulnerability, also known as a \"billion laughs\" style denial of service.\n\n### Example payload\n\n```yaml\nopenapi: 3.0.0\ninfo:\n  title: Test\n  version: 0.0.1\npaths: {}\nx-a: \u0026a [\"lol\", \"lol\", \"lol\", \"lol\", \"lol\", \"lol\", \"lol\", \"lol\", \"lol\"]\nx-b: \u0026b [*a, *a, *a, *a, *a, *a, *a, *a, *a]\nx-c: \u0026c [*b, *b, *b, *b, *b, *b, *b, *b, *b]\nx-d: \u0026d [*c, *c, *c, *c, *c, *c, *c, *c, *c]\nx-e: \u0026e [*d, *d, *d, *d, *d, *d, *d, *d, *d]\nx-f: \u0026f [*e, *e, *e, *e, *e, *e, *e, *e, *e]\n```\n\n## Remediation\n\nUsers should upgrade to Microsoft.OpenApi.YamlReader `2.12.0` or `3.10.0`, or Microsoft.OpenApi.Readers `1.6.30`, depending on the major version line they consume.\n\nThe patched versions bound YAML-to-JSON conversion work and fail fast instead of allowing unbounded expansion. The default limits are:\n\n* Maximum materialized node count: `5,000,000`\n* Maximum nesting depth: `64`\n\nWhen the limits are exceeded, `OpenApiYamlReader.Read` reports an `OpenApiDiagnostic` error and does not return a parsed document.\n\nThe limits are exposed as process-wide static properties on `YamlConverter` for consumers that need to tune them for trusted workloads:\n\n* `YamlConverter.MaxNodeCount`\n* `YamlConverter.MaxDepth`\n\nApplications 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.",
  "id": "GHSA-7pxr-59rr-hqj2",
  "modified": "2026-10-14T20:11:30Z",
  "published": "2026-10-14T20:11:29Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/security/advisories/GHSA-7pxr-59rr-hqj2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72923"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/pull/3000"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/pull/3005"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/pull/3020"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/commit/1f9aea9bdcbf4066b59ce33b3bd8f97ed9cb4766"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/commit/21793261d6860fb6e607b71fd95c0bd320724764"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/commit/4db9af07d112cdf45170b7a946f956ffe74fa14e"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/microsoft/OpenAPI.NET"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/releases/tag/v1.6.30"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/releases/tag/v2.12.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/microsoft/OpenAPI.NET/releases/tag/v3.10.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Microsoft.OpenApi.YamlReader vulnerable to denial of service via YAML alias expansion"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-72923 (GCVE-0-2026-72923)

FKIE_CVE-2026-72923

GHSA-7PXR-59RR-HQJ2

Impact

Affected versions

Microsoft.OpenApi.YamlReader

Microsoft.OpenApi.Readers

Patches

Impact

Details

Example payload

Remediation

Tags

Sightings

Nomenclature

Vulnerability timeline

Related by attack behaviour