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Movable TypeApplication · Sixapart

CVE-2021-20815

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 Edit Boilerplate 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 · moderate confidence

A stored cross-site scripting (XSS) vulnerability exists in the Edit Boilerplate screen of Movable Type. Attackers can inject malicious script or HTML content that gets stored and executed when other users view the affected screen.

MitigationUpdate to Movable Type 7 r.4904+, Movable Type 6.8.1+, or Movable Type Premium 1.45+ as specified in vendor advisories. If immediate patching is not possible, implement output encoding and input validation on the Edit Boilerplate 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. Locate Movable Type installation
    Search for mt-config.cgi file or typical installation directories such as /cgi-bin/mt/, /mt/, or check the web root for Movable Type files.
    Affected if Movable Type is not found on the system, then this CVE does not apply.
  2. Identify Movable Type version
    Open the admin dashboard and navigate to the system overview or tools section to view the version number. Alternatively, check the version file in the installation directory (often named VERSION or lib/MT.pm).
    Affected if Unable to determine the version, making it unclear whether the installation is affected.
  3. Compare installed version to affected ranges
    Match your identified version against: <= 1.44, >= 6.0 through 6.8.0, or >= 7.0 through 7.8.0 (excluding 7.8.0 and later).
    Affected if The installed version falls within one of these ranges: 1.44 or lower, 6.0 to 6.8.0, or 7.0 to 7.8.0.
  4. Verify Edit Boilerplate functionality access
    Log into Movable Type as an administrator or template editor and confirm access to the Edit Boilerplate screen under the Templates or Design section.
    Affected if The Edit Boilerplate screen is accessible and the version is within the affected ranges, the environment is vulnerable to stored XSS.

The environment is affected if Movable Type is installed with a version in the ranges <= 1.44, 6.0-6.8.0, or 7.0-7.8.0 and users have access to the Edit Boilerplate functionality.

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

Update to Movable Type 7 r.4904+, Movable Type 6.8.1+, or Movable Type Premium 1.45+ as specified in vendor advisories. If immediate patching is not possible, implement output encoding and input validation on the Edit Boilerplate functionality.

Recommended fix High confidence

Movable Type 7: 7.8.0+; Movable Type 6: 6.8.1+; Movable Type Premium: 1.45+

  1. 1. Identify the current Movable Type version installed (check mt-config.cgi or the system information screen)
  2. 2. For Movable Type 7 series (versions 7.0 to 7.7.x): upgrade to version 7.8.0 or later
  3. 3. For Movable Type 6 series (versions 6.0 to 6.8.0): upgrade to version 6.8.1 or later
  4. 4. For Movable Type Premium (versions up to 1.44): upgrade to version 1.45 or later
  5. 5. Verify the upgrade was successful by checking the version number in the admin interface
  6. 6. Test the Edit Boilerplate screen to confirm the XSS vulnerability is remediated
Caveat Review migration guides when upgrading across major version jumps; test custom templates and plugins for compatibility

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
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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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-2021-20815 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