CVE-2021-20665
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 · uneditedCross-site scripting vulnerability in in Add asset screen of Contents field of Movable Type 7 r.4705 and earlier (Movable Type 7 Series), Movable Type Advanced 7 r.4705 and earlier (Movable Type Advanced 7 Series), Movable Type Premium 1.39 and earlier, and Movable Type Premium Advanced 1.39 and earlier allows remote attackers to inject an arbitrary script via unspecified vectors.
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 confidenceA reflected cross-site scripting (XSS) vulnerability exists in the Add asset screen of the Contents field in Movable Type 7 r.4705 and earlier, Movable Type Advanced 7 r.4705 and earlier, and Movable Type Premium versions 1.39 and earlier. Attackers can inject arbitrary JavaScript through unspecified vectors.
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<= 7.4705<= 7.4705<= 1.39<= 1.39CVSS 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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Check Movable Type version installedAccess the Movable Type admin dashboard and navigate to System Overview or Help > Version, or check the version number in the mt-config.cgi file or the MT version file in the installation directoryAffected if The version displayed is 7.4705 or earlier for Movable Type/Movable Type Advanced, or 1.39 or earlier for Movable Type Premium/Premium Advanced
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Verify if Contents field Add Asset feature is accessibleLog into the Movable Type admin panel, create or edit a content type or entry that contains a Contents field, then navigate to the Add Asset screen within that Contents fieldAffected if The Add Asset screen in a Contents field is accessible and functional in the installation
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Confirm Content Security Policy headers are not implementedInspect HTTP response headers from the Movable Type admin pages by using browser developer tools, curl -I command, or a header inspection tool, looking for Content-Security-Policy or X-Content-Security-Policy headersAffected if No Content-Security-Policy headers are present on the Movable Type admin pages
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Identify if user-supplied content in Contents field is unsanitizedAttempt to insert a benign test script tag (e.g., <script>alert('test')</script>) into a Contents field via the Add Asset screen and observe if it executes or is reflected in the response without encodingAffected if The script tag is reflected unescaped in the page output, indicating the XSS vulnerability is present
The environment is affected if Movable Type version is 7.4705 or earlier (or Premium 1.39 or earlier) AND the Add Asset screen in the Contents field is accessible without sanitization or CSP protection in place.
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 Movable Type 7 r.4706 or later, or Movable Type Premium 1.40 or later. Until patched, sanitize all user-supplied content in the Contents field and implement Content Security Policy headers.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20665 — 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-2021-20665 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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