CVE-2009-4444
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 · uneditedMicrosoft Internet Information Services (IIS) 5.x and 6.x uses only the portion of a filename before a ; (semicolon) character to determine the file extension, which allows remote attackers to bypass intended extension restrictions of third-party upload applications via a filename with a (1) .asp, (2) .cer, or (3) .asa first extension, followed by a semicolon and a safe extension, as demonstrated by the use of asp.dll to handle a .asp;.jpg file.
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 confidenceMicrosoft IIS 5.x and 6.x incorrectly parses filenames by using only the portion before a semicolon (;) to determine the file extension. This allows attackers to bypass extension restrictions in third-party upload applications by uploading files named 'malicious.asp;.jpg', which IIS then processes using the ASP handler (asp.dll) instead of treating the file as a benign JPG image.
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= 5.0= 6.0CVSS 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
- M
- Authentication
- Single
- Confidentiality
- Partial
- Integrity
- Partial
- Availability
- Partial
AV:N/AC:M/Au:S/C:P/I:P/A:P
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 IIS versionRun 'inetmgr' to open IIS Manager, or check the Windows version via 'winver', then check IIS version in the About box (IIS Manager > Help > About). Alternatively, check the 'httperr' logs or the IIS metabase for the version number.Affected if The installed version is Microsoft IIS 5.0 or 6.0 specifically.
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Locate web applications with file upload functionalitySearch the web root directory for ASP.NET or classic ASP scripts that handle file uploads (look for forms with enctype='multipart/form-data' and server-side code that processes the 'File' or 'PostedFile' object).Affected if A web application exists that accepts file uploads from users.
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Inspect uploaded files for semicolon in filenameSearch the web directories (especially upload folders) for files containing a semicolon in the name using the command: dir /s /b C:\inetpub\wwwroot\*;*.* (adjust path to match web root).Affected if Files with semicolons in the filename (e.g., 'shell.asp;.jpg') are present on the server.
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Check for ASP files with unusual extensionsReview .asp files in web directories for unexpected file types. Use: Get-ChildItem -Recurse -Filter *.asp | Select-Object FullName in PowerShell.Affected if ASP files exist with double extensions or in directories not designated for active script execution.
A system is affected if it runs IIS 5.0 or 6.0 AND hosts a web application with file upload capability, as the semicolon parsing bypass could allow malicious file execution.
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 dataUpgrade to IIS 7.0 or later which properly handles semicolons in filenames, or configure Request Filtering in IIS to deny URLs containing semicolons; also implement server-side content-type and magic-byte validation beyond extension checking for uploaded files.
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2009-4444 — 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-2009-4444 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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- 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