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The vulnerability resides within Microsoft.OpenApi.YamlReader and Microsoft.OpenApi.Readers libraries, which utilize SharpYaml to parse YAML-based OpenAPI specifications. SharpYaml parses YAML documents by representing anchors and aliases as shared nodes inside a directed acyclic graph, keeping initial memory consumption minimal. However, during the conversion process from the YAML graph into System.Text.Json.Nodes.JsonNode objects, aliases must be fully materialized as independent nodes because individual JsonNode instances cannot be attached to multiple parents. Without bounded limits on this conversion phase, a specially crafted small YAML document containing deeply nested anchors and aliases forces an exponential expansion. When N nested anchors are each referenced k times, the transformation requires up to k^N materialized nodes. This results in intensive memory exhaustion, triggering out-of-memory errors and terminating the host application process via a classic “billion laughs” style denial of service vector.
DailyCVE Form:
Platform: Microsoft .NET
Version: 2.0.0-3.10.0
Vulnerability : Uncontrolled Resource
Severity: Critical
date: 2026-09-08
Prediction: 2026-09-08
What Undercode Say
Analytics
The vulnerability stems from the discrepancy between how YAML parsers handle memory representation via directed acyclic graphs and how target JSON structures demand independent node allocation. Because the deserialization layer fails to enforce recursion bounds or maximum node thresholds by default, malicious payloads can induce exponential memory growth within milliseconds of ingestion. Systems processing untrusted OpenAPI specs synchronously are prone to sudden application crashes without throwing catchable exceptions.
Exploit: (Educational Purposes!)
openapi: 3.0.0
info:
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]
Protection: from this CVE
Upgrade affected packages immediately to Microsoft.OpenApi.YamlReader versions 2.12.0 or 3.10.0, or Microsoft.OpenApi.Readers version 1.6.30 or higher. These patched releases enforce strict limits on maximum node count (defaulting to 5,000,000) and maximum nesting depth (defaulting to 64) via static properties like YamlConverter.MaxNodeCount and YamlConverter.MaxDepth. Additionally, isolate parsing operations for untrusted input within separate worker processes to contain potential denial-of-service impacts.
Impact
Successful exploitation leads strictly to availability loss and application process termination due to excessive memory allocation and out-of-memory exceptions. The vulnerability does not allow remote code execution, authentication bypass, data exposure, or privilege escalation.
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Sources:
Reported By: github.com
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