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Movable TypeApplication · Sixapart

CVE-2021-20811

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 List of Assets 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 confidence

Cross-site scripting (XSS) vulnerability in the List of Assets screen of Movable Type allows remote attackers to inject arbitrary script or HTML via unspecified vectors. The vulnerability stems from insufficient input sanitization or output encoding in user-supplied content displayed in the asset listing interface.

MitigationApply vendor patches for the specific Movable Type versions (r.4904+ for MT7, 6.8.1+ for MT6) to address the XSS vulnerability in the asset listing functionality.

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 version
    Locate the Movable Type installation and check the version file or admin interface for the installed version number (typically found in mt-config.cgi, the MT admin dashboard, or version.pm in the lib directory)
    Affected if The installed version falls outside these safe versions: 6.0.1 through 6.8.0 (MT6), 7.0.0 through 7.7.x (MT7), or is 1.44 or earlier (MT1.x)
  2. Confirm asset listing functionality is accessible
    Navigate to the List of Assets screen in the Movable Type admin interface (usually found under the Assets menu in the system)
    Affected if The asset listing interface is accessible to the user being assessed (the vulnerability can be triggered by any user who can access this screen)
  3. Check for existing assets with user-supplied metadata
    Review existing assets in the system for any that contain user-supplied filenames, descriptions, or other metadata that could contain script tags
    Affected if There are assets with user-supplied content (such as uploaded files with custom names, descriptions, or tags) displayed in the asset listing
  4. Verify asset thumbnails or previews render HTML
    Observe whether the asset listing renders thumbnails, filenames, or descriptions directly without visible encoding (view page source if needed to check for unencoded characters)
    Affected if The asset listing displays raw or improperly escaped user-supplied content in filenames, descriptions, or other metadata fields

A user is affected if they run Movable Type versions 1.44 or earlier, 6.0.1 through 6.8.0, or 7.0.0 through 7.7.x AND have access to the asset listing screen with assets containing user-supplied content that may be displayed without proper encoding.

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 vendor patches for the specific Movable Type versions (r.4904+ for MT7, 6.8.1+ for MT6) to address the XSS vulnerability in the asset listing functionality.

Recommended fix High confidence

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

  1. 1. Back up your Movable Type installation, including the database and all files.
  2. 2. Identify your current Movable Type version (6.x, 7.x, Premium, or Advanced).
  3. 3. For Movable Type 7 Series: upgrade to version 7.8.0 or later.
  4. 4. For Movable Type 6 Series: upgrade to version 6.8.1 or later.
  5. 5. For Movable Type Premium: upgrade to version 1.45 or later.
  6. 6. For Movable Type Premium Advanced: upgrade to version 1.45 or later.
  7. 7. After upgrading, verify the List of Assets screen functions correctly and the XSS vulnerability is remediated.
Caveat Review release notes for your specific version series for any configuration or template changes; minor version upgrades typically have minimal breaking changes

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

Fix this in Movable Type Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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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-2021-20811 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