CVE-2021-20664
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 Asset registration screen 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 6.7.5 and earlier (Movable Type 6.7 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 confidenceCross-site scripting (XSS) vulnerability in the asset registration screen of Movable Type allows remote attackers to inject arbitrary JavaScript through unsanitized user input. This is a stored XSS issue where malicious scripts can be embedded in asset metadata and executed when other users view the affected content.
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<= 6.7.5>= 7.0000, <= 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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Identify Movable Type versionLocate the version file or admin dashboard that displays the installed Movable Type version. Common locations include the admin interface footer, a version.php file in the installation directory, or system information page.Affected if The installed version falls within any of these ranges: Movable Type <= 6.7.5, Movable Type 7.x <= 7.4705, Movable Type Premium <= 1.39, or Movable Type Premium Advanced <= 1.39
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Confirm asset registration feature accessLog into the Movable Type admin panel and navigate to the asset management section. Verify that the asset registration/upload functionality is available and accessible.Affected if The asset registration screen is accessible to the user account being tested
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Inspect asset metadata input fieldsUsing a browser developer console or HTTP proxy, observe the asset registration process. Examine the HTML form fields where asset metadata (filename, description, caption, tags) can be entered and submitted.Affected if Input fields for asset metadata do not appear to have visible output encoding or validation indicators
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Review asset display outputAfter uploading a test asset with metadata containing special characters, view the asset in the front-end or admin interface to see how the metadata is rendered.Affected if The asset metadata is rendered without visible sanitization or encoding when displayed to other users
A user is affected if they are running any Movable Type version within the ranges listed and have the asset registration feature accessible to users who could potentially inject malicious scripts.
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 dataImplement input validation and output encoding for all user-supplied data in the asset registration functionality; upgrade to versions beyond r.4705 for Movable Type 7/Advanced 7, beyond 6.7.5 for Movable Type 6.7, and beyond 1.39 for Premium variants.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-20664 — 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-2021-20664 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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