CVE-2021-20808
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 Search 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 Search screen of Movable Type allows remote attackers to inject arbitrary JavaScript or HTML via unsanitized user input in search parameters.
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 and read the version file in your Movable Type installation - typically found in the mt-version file in the root directory or lib/MT.pmAffected if Version is <= 1.44, OR >= 6.0 through 6.8.0, OR >= 7.0 through 7.8.0 (Movable Type Premium versions before 1.45 are also affected)
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Confirm Search functionality is enabledVerify the Movable Type search module is installed and accessible - check for mt-search.cgi in the cgi-bin directory or confirm the Search screen is available in the admin interfaceAffected if The Search feature is enabled and accessible to end users
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Test search parameter handlingSubmit a benign test string containing HTML characters (such as <script>alert(1)</script>) to the search endpoint and inspect whether these characters are reflected back unsanitized in the responseAffected if The search input is reflected in the page output without proper HTML encoding or sanitization
You are affected if your installed Movable Type version falls within the vulnerable ranges AND the Search screen is accessible without proper input sanitization on your system.
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.
dbcve · scoped7.8.0
Update Movable Type to the patched version (Movable Type 7 r.4904 or later, Movable Type 6.8.1 or later, or Movable Type Premium 1.45 or later) to receive the vendor patch for input sanitization on the Search screen.
Movable Type 7.8.0 or later (MT7 series); Movable Type 6.8.1 or later (MT6 series); Movable Type Premium 1.45 or later
- Backup your Movable Type database and all application files before proceeding with any upgrade.
- Download the latest Movable Type 7.x release (7.8.0 or later) from the official Movabletype.org website.
- For Movable Type 6 Series users: Download version 6.8.1 or later.
- For Movable Type Premium users: Upgrade to version 1.45 or later which contains the security fix.
- Follow the standard Movable Type upgrade instructions: stop the web server, replace the core MT files, run the upgrade script via browser, then restart the web server.
- Clear all caches and rebuild the website after upgrade to ensure all templates are updated.
- Verify the fix by checking that the Search screen properly sanitizes user input and does not allow script execution.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20808 — 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-2021-20808 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