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CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.
Exact risk observation. Current source statements above are a separate evidence layer. Latest risk evidence.
No KEV entry is attached to this observation; this is not evidence that exploitation is absent.
FIRST EPSS: 1.90 % · percentile 79.54 % · scored 28 Oct 2026. Retained older prediction.
Observed 28 Oct 2026 19:55:37 UTC · Complete immutable risk JSON
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.
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
datePublished: Sep 8, 2026, 5:12:20 PM
dateUpdated: Oct 14, 2026, 8:08:53 PM
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.
EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Deferred
Weakness classifications: CWE-400
published: 2026-09-08T18:20:16.310
lastModified: 2026-10-14T21:17:39.323
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
### 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 ```yaml 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.
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Publisher rating · HIGH