CVE-2026-23666
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedImproper input validation in .NET Framework allows an unauthorized attacker to deny service over a network.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceImproper input validation vulnerability in .NET Framework allows unauthenticated remote attackers to cause denial of service by sending specially crafted network requests that trigger the validation failure.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 3.5= 4.7.2= 4.8= 4.8.1= 4.6.2= 4.7= 4.7.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed .NET Framework versionOpen Registry Editor and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full (for .NET 4.x) or HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v3.5 for .NET 3.5. Check the 'Version' value in the right pane.Affected if The installed version matches 3.5, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1, or 4.8 exactly.
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Verify .NET Framework network services are runningOpen Command Prompt and run 'netstat -an | findstr LISTENING' to list all listening network ports. Identify any services binding to network interfaces (0.0.0.0 or specific IP addresses) that rely on .NET Framework.Affected if The system has .NET Framework-based services listening on network ports (TCP/UDP) and the installed version is among the affected versions.
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Identify .NET-based applications with network exposureReview installed applications and services that use .NET Framework. Check IIS if present: open IIS Manager, expand Sites, and note any bindings. Use 'wmic service get name,displayname,startmode,state' to list services and cross-reference with .NET applications.Affected if There are ASP.NET web applications, WCF services, or other .NET executables exposed to network requests on affected versions.
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Check for vulnerable network endpointsIf using IIS, examine web.config files in site root directories for handler mappings and request processing configuration. For self-hosted .NET services, review app.config files for system.serviceModel bindings that expose network endpoints.Affected if The system exposes HTTP, TCP, or other network endpoints through .NET Framework components and the version is affected.
A system is affected if it runs any version of .NET Framework matching 3.5, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1, or 4.8 AND has network-accessible endpoints or services built on .NET Framework that can receive the specially crafted requests.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply Microsoft security updates for .NET Framework when released. Implement input validation layers and rate limiting as compensating controls until patch is available.
- Consultation2.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,480.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-23666 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-23666 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data