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.net FrameworkApplication · Microsoft

CVE-2014-4121

HIGH · 10.0 CVSS v2.0 Published 2014-10-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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
Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4, 4.5, 4.5.1, and 4.5.2 does not properly parse internationalized resource identifiers, which allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via a crafted request to a .NET web application, aka ".NET Framework Remote Code Execution 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 · high confidence

Microsoft .NET Framework fails to properly validate internationalized resource identifiers (IRIs) in web requests, allowing specially crafted input to trigger memory corruption. An attacker sending a malicious IRI-formatted request to a .NET web application can achieve remote code execution or cause a denial of service.

MitigationApply Microsoft security update MS14-066 (or subsequent superseded patches) to all affected .NET Framework installations. For systems awaiting patching, implement WAF rules blocking requests with unusual Unicode characters in resource paths and validate all IRI input server-side.

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:= 2.0= 3.5= 3.5.1= 4.0= 4.5= 4.5.1= 4.5.2

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
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:L/Au:N/C:C/I:C/A:C

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\v\Full (or use 'Get-ItemProperty HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full' in PowerShell). Check the Release value to determine the installed version.
    Affected if The installed version matches 2.0, 3.5, 3.5.1, 4.0, 4.5, 4.5.1, or 4.5.2 exactly.
  2. Determine if IIS with ASP.NET is enabled
    Check if Internet Information Services (IIS) is installed and the ASP.NET role service is enabled. In PowerShell, run: Get-WindowsOptionalFeature -Online | Where-Object {$_.FeatureName -like '*ASP.NET*'}. Alternatively, check for the presence of aspnet_isapi.dll in the IIS script mappings.
    Affected if IIS with ASP.NET is installed and the web server is processing .NET web requests.
  3. Identify web applications handling request paths
    Review the web.config files in any ASP.NET applications hosted on the server. Check for URL routing modules or custom HTTP handlers that process resource paths from incoming requests.
    Affected if The server hosts ASP.NET web applications that accept and process URL paths from external requests.
  4. Verify IRI handling is in use
    Examine application logs and IIS logs for requests containing non-ASCII characters or Unicode sequences in the URL path (such as % encoded characters or internationalized domain names in paths).
    Affected if The application processes URLs with internationalized characters or the system shows recent web traffic with IRI-formatted paths.
  5. Confirm network exposure of affected component
    Determine if the ASP.NET web applications are accessible over the network. Check IIS bindings and firewall rules to confirm the web server accepts external HTTP/HTTPS requests.
    Affected if The .NET web applications are reachable from untrusted networks.

The system is affected if it runs any of the listed .NET Framework versions (2.0, 3.5, 3.5.1, 4.0, 4.5, 4.5.1, or 4.5.2) and hosts ASP.NET web applications accessible over a network that process incoming request paths.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Microsoft security update MS14-066 (or subsequent superseded patches) to all affected .NET Framework installations. For systems awaiting patching, implement WAF rules blocking requests with unusual Unicode characters in resource paths and validate all IRI input server-side.

Recommended fix Moderate confidence
  1. Locate the Microsoft Security Bulletin MS14-066 and associated KB2999226 patch for your specific .NET Framework version
  2. Apply the security update through Windows Update or download from Microsoft Download Center
  3. Restart affected services or servers as required by the update
  4. Verify the patch installation by checking the installed updates in Control Panel > Programs and Features > View installed updates
  5. Test .NET web applications to ensure normal functionality after the update

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

Fix this in .net Framework Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,840
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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-2014-4121 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