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Movable TypeApplication · Sixapart

CVE-2021-20809

MEDIUM · 6.1 CVSS v3.1 Published 2021-08-26
Fix available
A fix is available. Upgrade to 7.8.0 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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 · unedited
Cross-site scripting vulnerability in Create screens of Entry, Page, and Content Type 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 · moderate confidence

A stored cross-site scripting (XSS) vulnerability exists in Movable Type's admin interface within the Create screens for Entry, Page, and Content Type modules. Attackers can inject malicious JavaScript or HTML through unspecified input fields when creating or editing content, which then executes when other users view the affected content in the admin panel or public-facing pages.

MitigationApply proper output encoding and input sanitization to all user-supplied fields in the Entry, Page, and Content Type creation forms. Validate and sanitize all content before storage and before rendering.

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
Movable TypeApplication
Affected:<= 1.44>= 6.0, <= 6.8.0>= 7.0, < 7.8.0

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify Movable Type installation
    Check for Movable Type by looking for its characteristic directory structure (mt-static, cgi-bin/mt), or by accessing the admin login page (typically at /mt/ or /cgi-bin/mt/)
    Affected if Movable Type is not present on the system
  2. Determine installed version
    Check the version number by looking at the mt-static/js/mt.js file, the MT::VERSION constant in the codebase, or the version displayed on the admin login page
    Affected if The installed version falls within <= 1.44, OR >= 6.0 and <= 6.8.0, OR >= 7.0 and < 7.8.0
  3. Confirm admin access is enabled
    Verify the Movable Type admin interface is accessible and functional by attempting to access the admin login page
    Affected if The admin panel is accessible and functional
  4. Check for content creation capability
    Verify whether users have the ability to create or edit Entry, Page, or Content Type content through the admin interface by logging in and checking permissions
    Affected if Users have author, editor, or admin privileges allowing content creation or editing in the admin panel
  5. Inspect for existing malicious content
    Review the database tables for Entries (mt_entry), Pages (mt_page), and Content Type records (mt_cd_*) for any suspicious script tags, event handlers, or unusual HTML in title, body, or custom field columns
    Affected if Any Entry, Page, or Content Type records contain unsanitized JavaScript or HTML tags

A user is affected if Movable Type is installed with a version matching <= 1.44, >= 6.0 through <= 6.8.0, or >= 7.0 through < 7.8.0, AND the admin interface is accessible allowing content creation or editing of Entries, Pages, or Content Types.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 7.8.0 or later
Fixed in 7.8.0
Interim mitigation

Apply proper output encoding and input sanitization to all user-supplied fields in the Entry, Page, and Content Type creation forms. Validate and sanitize all content before storage and before rendering.

Recommended fix High confidence

Movable Type 7.8.0+ (for 7.x series), 6.8.1+ (for 6.x series), 1.45+ (for Premium variants)

  1. 1. Identify your current Movable Type installation version and series (6.x, 7.x, Premium, or Premium Advanced)
  2. 2. For Movable Type 7 series: Upgrade to version 7.8.0 or later
  3. 3. For Movable Type 6 series: Upgrade to version 6.8.1 or later (the next security update after 6.8.0)
  4. 4. For Movable Type Premium: Upgrade to version 1.45 or later
  5. 5. For Movable Type Premium Advanced: Upgrade to version 1.45 or later
  6. 6. After upgrading, verify the fix by testing the Create screens for Entry, Page, and Content Type
  7. 7. Ensure custom plugins or templates are compatible with the new version before deploying to production
Caveat Review plugin and template compatibility before upgrading; test in staging environment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Movable Type Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20809 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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