EUVD-2026-40365
GHSA-v5pm-xwqc-g5wc
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
-
AccessIdentify service that parses uploaded OpenAPI specs
-
DeliveryCraft document with circular A↔B $ref
-
ExploitSubmit document to reader API
-
ExecutionTrigger unbounded recursion in resolver
-
PersistStack overflow terminates process
-
ImpactDenial of service
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Recursion depth limits
|
| Exploitation Conditions | The vulnerable application must parse an attacker-supplied OpenAPI document in-process through the public OpenAPI.NET reader APIs (JSON or YAML reader path) using an affected version (2.0.0-preview11-2.7.4 or 3.0.0-3.5.3). The specific trigger is an OpenAPI document containing a circular schema reference where one $ref resolves to another $ref pointing back (e.g., components.schemas.A → B and B → A). The CVSS vector is AV:N/AC:L/PR:N/UI:N, so no authentication or user interaction is needed at the parser level; the practical limiting factor is that the deployment must actually accept and parse untrusted/externally-sourced OpenAPI documents - installations that parse only their own trusted specs are not realistically exposed. The 1.x line is not exploitable. |
| Impact | Signals are largely consistent in direction but modest in real-world severity. The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, 7.5 High) reflects pure availability impact - no confidentiality or integrity loss - which matches the vendor's explicit statement that there is no RCE, auth bypass, privilege escalation, or data exposure. The supplied Tags ('Authentication Bypass, Privilege Escalation, RCE, Information Disclosure') directly CONTRADICT the authoritative description and CVSS C:N/I:N and should be treated as inaccurate generic labeling, not as evidence of broader impact. No EPSS score, KEV listing, or SSVC decision data was provided. There is no KEV entry, so this is not confirmed actively exploited; however the advisory publishes a trivial, deterministic reproduction payload, lowering the practical barrier to triggering it. The key real-world limiter is the precondition that the affected application must parse OpenAPI documents from untrusted sources in-process - many deployments only parse their own trusted specs, which sharply narrows exposure despite the network attack vector. |
| Exploit ScenarioDerived | An attacker submits a small crafted OpenAPI/Swagger document - for example, schemas A and B that $ref each other - to a service, CLI, or developer tool that parses uploaded OpenAPI specs in-process using Microsoft.OpenApi. Parsing recurses without bound, overflows the stack, and terminates the process, denying service to all users of that instance. A ready-to-use reproduction payload is published in the GitHub advisory, and low attack complexity (AC:L) plus no required privileges (PR:N) make triggering trivial wherever untrusted documents are accepted. |
Get an e-mail when this CVE is exploited, patched or re-scored. Free account.
Alert meAnalysisAIv1 – Jun 30, 2026
Denial of service in the Microsoft.OpenApi (OpenAPI.NET) .NET library lets a crafted OpenAPI document with circular schema $ref references crash the host process via stack overflow (CWE-674, uncontrolled recursion). Any .NET application, CLI, developer tool, or service that parses untrusted OpenAPI documents in-process through the public reader APIs is affected across both JSON and YAML reader paths, including Microsoft's own kiota tool. A working reproduction payload is published in the GitHub advisory; the impact is availability-only with no code execution, and there is no public exploit identified beyond that payload and no evidence of active exploitation.
RemediationAI
Vendor-released patch: upgrade Microsoft.OpenApi to 2.7.5 or later on the 2.x line, or to 3.5.4 or later on the 3.x line, matching whichever major version your project consumes; rebuild and redeploy downstream consumers such as kiota against the patched package. Where immediate upgrade is not possible and the application must parse OpenAPI documents from untrusted sources, move the parsing out of the primary application process and into an isolated/sandboxed worker process so a stack-overflow crash only kills the worker and not the main service (trade-off: added IPC complexity and latency); alternatively, restrict the parser to trusted, first-party OpenAPI documents and reject or size/structure-validate externally supplied specs before parsing (trade-off: blocks legitimate untrusted-input use cases). Full guidance is in the advisory at https://github.com/microsoft/OpenAPI.NET/security/advisories/GHSA-v5pm-xwqc-g5wc.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 3 packages in nuget, euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Microsoft.OpenApi is a Microsoft-maintained NuGet library (pkg:nuget/microsoft.openapi) that reads, writes, and models OpenAPI/Swagger specification documents for the .NET ecosystem; it underpins tooling such as microsoft/kiota and broader API/SDK generation workflows. The root cause is CWE-674 (Uncontrolled Recursion): when the reader resolves a $ref that points to another $ref, two schemas that reference each other (A→B and B→A) drive the reference-resolution logic into unbounded recursion, exhausting the thread stack and terminating the process. The flaw is specific to the reference-resolution behavior introduced from the 2.x preview line onward - the 1.x line is not affected because it could not resolve a reference that pointed to another reference. Both the core JSON reader and the Microsoft.OpenApi.YamlReader path exhibit the behavior.
Know when the next one hits your stack
- Watch products and get an email when something new is published
- Check this CVE against your own stack and servers
- Exploit and PoC references, threat intelligence from 22 sources
No credit card · 7-day full trial
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-deliverable document with trivial deterministic payload (AV:N/AC:L/PR:N/UI:N); availability-only process crash gives A:H with C:N/I:N and unchanged scope.
Primary rating from Vendor (https://github.com/microsoft/OpenAPI.NET).
CVSS VectorVendor: https://github.com/microsoft/OpenAPI.NET
Lifecycle Timeline
2DescriptionCVE.org
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
{
"openapi": "3.0.0",
"info": {
"title": "Test",
"version": "0.0.1"
},
"paths": {},
"components": {
"schemas": {
"A": {
"$ref": "#/components/schemas/B"
},
"B": {
"$ref": "#/components/schemas/A"
}
}
}
}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.
Executive ViewAI
The Microsoft.OpenApi (.NET) library contains a denial-of-service vulnerability (CVE-2026-49451, CVSS 7.5) affecting any .NET application that parses untrusted OpenAPI documents, including Microsoft's kiota tool. Publicly available exploit code exists in the form of a reproducible payload in the GitHub advisory; there is no evidence of active exploitation. An attacker can trigger a stack overflow by submitting a malformed OpenAPI document with circular schema references, crashing the affected application and causing service outages-a critical availability risk for all internal and external .NET services relying on OpenAPI document ingestion.
No vendor-released patch identified at time of analysis. Interim mitigations: (1) Input validation to reject OpenAPI documents with circular $ref references before processing; (2) Execute OpenAPI parsers in isolated processes or containers to limit DoS impact; (3) Restrict OpenAPI document sources to pre-approved/validated inputs only; (4) Implement network rate limiting on document submission endpoints; (5) Enhanced monitoring for unexpected process crashes in .NET services and kiota deployments; (6) Deploy API gateway filtering for external OpenAPI document sources.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Privilege escalation occurs when an attacker leverages flaws in access control mechanisms to gain permissions beyond what they were originally granted.
Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.
Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.
Exploit-DB