CVE-2021-20810
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 Website Management screen of Movable Type (Movable Type 7 r.4903 and earlier (Movable Type 7 Series), Movable Type 6.8.0 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.4903 and earlier (Movable Type Advanced 7 Series), Movable Type Premium 1.44 and earlier, and Movable Type Premium Advanced 1.44 and earlier) allows remote attackers to inject arbitrary script or HTML 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 · high confidenceCross-site scripting (XSS) vulnerability in the Website Management screen of Movable Type allows remote attackers to inject arbitrary JavaScript or HTML through unspecified vectors. This is a reflected XSS vulnerability (CVSS 6.1) affecting multiple product lines including Movable Type 7, 6, Premium, and Premium Advanced versions.
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<= 1.44>= 6.0, <= 6.8.0>= 7.0, < 7.8.0CVSS 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
- 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 in your Movable Type installation. Check mt-config.cgi or the version file typically found in the MT directory (often lib/MT.pm or a VERSION file in the root installation folder). Look for a line displaying the version number.Affected if version falls within these ranges: 6.0 to 6.8.0, 7.0 to 7.8.0, or versions 1.44 and below
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Confirm Movable Type product lineIdentify whether you are running Movable Type 6, Movable Type 7, Movable Type Premium, or Movable Type Premium Advanced. The product name is usually visible in the admin dashboard footer or in the mt-config.cgi configuration file.Affected if product is any of the four affected lines: Movable Type 6, Movable Type 7, Movable Type Premium, or Movable Type Premium Advanced
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Check if admin interface is accessibleVerify that the Movable Type administrator interface (mt.cgi) or the newer mt-admin path is accessible from your web server. Attempt to access the /mt/ or /cgi-bin/mt/ admin path in a browser.Affected if the administrative web interface is accessible to users (even if password-protected, the XSS triggers on the Website Management screen)
You are affected if you are running Movable Type 6.x (6.0-6.8.0), 7.x (7.0-7.8.0), or Premium/Premium Advanced versions within the affected ranges and the admin interface is accessible.
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 data7.8.0
Apply available vendor patches for Movable Type. Until patched, restrict administrative access to trusted users only and implement additional input validation on the Website Management screen.
- Consultation2.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20810 — 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-2021-20810 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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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.
- 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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