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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 May 2022.
.net FrameworkApplication · Microsoft

CVE-2020-0646

CRITICAL · 9.8 CVSS v3.1 Published 2020-01-14
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Public exploit Remotely reachable No privileges Zero-click Patch available

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 · unedited
A remote code execution vulnerability exists when the Microsoft .NET Framework fails to validate input properly, aka '.NET Framework Remote Code Execution Injection Vulnerability'.

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 confidence

This is a remote code execution vulnerability in Microsoft .NET Framework caused by improper input validation. Attackers can exploit this by submitting specially crafted input that bypasses validation checks, allowing arbitrary code execution on the targeted system.

MitigationApply Microsoft security updates for .NET Framework as soon as they become available; until then, restrict network exposure of affected systems and implement strict input validation as a defense-in-depth measure.

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
.net FrameworkApplication
Affected:= 3.0= 3.5= 4.6.2= 4.7= 4.7.1= 4.7.2= 4.8= 3.5.1= 4.5.2= 4.6= 4.6.1

CVSS 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
High
Integrity
High
Availability
High

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

Work through these to decide whether this CVE applies to you.

  1. Identify installed .NET Framework version
    Open 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\v3.0 (for .NET 3.0). Check the 'Version' value in each subkey. Alternatively, run 'Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full' -Name Version' in PowerShell.
    Affected if The installed version matches one of: 3.0, 3.5, 3.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, or 4.8 (or any version equal to these release numbers without subsequent security patches).
  2. Identify .NET applications accepting network input
    Review running services and IIS application pools. Use 'Get-Process | Where-Object {$_.ProcessName -like '*w3wp*' -or $_.ProcessName -like '*dotnet*'}' to list IIS worker processes and .NET processes. Check for any exposed WCF services, ASP.NET applications, or .NET remoting endpoints using 'netstat -ano | findstr LISTENING' to list listening ports.
    Affected if A .NET application or service is running and accepting network requests on any port.
  3. Check for XAML/XAMLX workflows or serialized input processing
    Review application configuration files (web.config, app.config) for System.WorkflowServices, XAML serialization settings, or any custom model binders. Inspect IIS logs and WCF trace logs for any unusual request patterns. Search project source code repositories for 'XamlReader.Load', 'XmlSerializer', or workflow-related endpoints.
    Affected if The application processes XAML, XAMLX workflows, or deserializes XML input from untrusted sources.

You are affected if your system runs any unpatched .NET Framework version matching 3.0 through 4.8 AND hosts a .NET application or service that accepts input from network sources.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch portal.msrc.microsoft.com →
Interim mitigation

Apply Microsoft security updates for .NET Framework as soon as they become available; until then, restrict network exposure of affected systems and implement strict input validation as a defense-in-depth measure.

Recommended fix High confidence

Apply Microsoft January 2020 security updates for .NET Framework (patches, not version upgrade)

  1. Open Windows Update on the affected system and check for available updates
  2. Install the January 2020 security updates for Microsoft .NET Framework
  3. For .NET Framework 3.5: Install the applicable January 2020 security update (e.g., KB4536952)
  4. For .NET Framework 4.6.2 and 4.7: Install the applicable January 2020 security update (e.g., KB4536953)
  5. Restart the system after applying the updates
  6. Verify the updates are installed by checking the installed updates list
Caveat Standard security update with minimal risk; test in staging if possible

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in .net Framework Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-0646 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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