CVE-2021-20103
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 · uneditedMachform prior to version 16 is vulnerable to stored cross-site scripting due to insufficient sanitization of file attachments uploaded with forms through upload.php.
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 confidenceMachform versions prior to 16 contain a stored XSS vulnerability in upload.php where file attachments submitted through forms are not properly sanitized. Attackers can upload malicious files containing embedded scripts that execute when other users view or interact with the uploaded content, leading to session hijacking or credential theft.
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< 16CVSS 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
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
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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Locate Machform installation and determine versionCheck your web server document root for the Machform directory, then look for a version file (commonly version.php, CHANGELOG, or the main index.php header) to identify the installed version numberAffected if The installed version number is less than 16 (e.g., 15.x, 14.x, etc.)
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Verify upload.php exists in the Machform directoryCheck for the presence of upload.php in the Machform web root directory - this is the specific file mentioned as containing the vulnerabilityAffected if upload.php exists and is accessible via the web server
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Confirm file upload functionality is enabledReview the Machform admin panel or configuration files to determine if any forms have file upload fields enabled, as the XSS only triggers when uploaded files are viewedAffected if File upload fields are enabled on any form and the upload directory is web-accessible
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Check upload directory configurationExamine the uploads folder permissions and configuration - verify if uploaded files are served with proper Content-Disposition headers or if the server allows MIME-sniffing of uploaded contentAffected if Uploaded files are served directly by the web server without Content-Disposition: attachment headers, allowing the browser to interpret them as executable content
Your environment is affected if Machform version is below 16, upload.php is accessible, and file upload forms are enabled with direct file serving that allows MIME-sniffing.
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 data16
Upgrade to Machform version 16 or later which implements proper sanitization of file attachments. Additionally, implement server-side file type validation and Content-Disposition headers to prevent MIME-sniffing attacks.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20103 — 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-2021-20103 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
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