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PloneApplication

CVE-2021-33511

HIGH · 7.5 CVSS v3.1 Published 2021-05-21
Fix available
A fix is available. Upgrade to after 5.2.4 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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
Plone though 5.2.4 allows SSRF via the lxml parser. This affects Diazo themes, Dexterity TTW schemas, and modeleditors in plone.app.theming, plone.app.dexterity, and plone.supermodel.

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

Plone through 5.2.4 contains a Server-Side Request Forgery (SSRF) vulnerability in the lxml parser affecting Diazo themes, Dexterity TTW schemas, and modeleditors. The lxml parser can be induced to make arbitrary HTTP requests to internal or external resources, potentially allowing attackers to access internal services, metadata endpoints, or cloud instance metadata.

MitigationUpgrade Plone to version 5.2.4 or later which contains the security patch. If immediate upgrade is not possible, restrict network access to the Plone server and disable or sandbox the lxml parser's external entity resolution capabilities.

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
PloneApplication
Affected:<= 5.2.4

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
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 installed Plone version
    Check the version.py file in the Plone installation directory or use the management interface to view the Plone version. Common locations include /path/to/plone/Plone/version.py or through the ZMI (Zope Management Interface) at /manage_main.
    Affected if The installed version is 5.2.4 or earlier (any version up to and including 5.2.4).
  2. Check if Diazo theming is enabled
    Inspect the site configuration or theme settings in the Plone control panel. Look for active Diazo theme assignments in the theming control panel or check the portal_theme tool via the ZMI at /portal_setup/manage.
    Affected if Diazo themes are active and the lxml parser is used to process theme XML/XSLT files.
  3. Identify if Dexterity TTW schemas are in use
    Access the Dexterity content types configuration through the Plone control panel (Site Setup > Content Types) or inspect the portal_types tool in the ZMI. Look for content types created through-the-web using Dexterity.
    Affected if Any Dexterity content types were created or modified through-the-web, which invokes the lxml parser for XML schema processing.
  4. Check for modeleditors usage
    Review the Plone configuration for any modeleditor implementations or custom content types using modeling features. Check the products.plone.modeleditor package if installed, or inspect content type definitions for model-based editors.
    Affected if Modeleditors are configured or any content types use model-driven forms that parse XML using lxml.
  5. Verify lxml parser is accessible to Plone
    Check if the lxml Python library is installed in the Plone environment by examining the Python packages (pip list or in the eggs directory) and confirm Plone has import access to lxml.xmlparser functionality.
    Affected if The lxml library is installed and available to Plone's runtime environment.

A system is affected if it runs Plone version 5.2.4 or earlier AND uses any Diazo themes, Dexterity TTW schemas, or modeleditors that invoke the lxml parser for XML processing.

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.

From vendor data
Upgrade available Upgrade to a release after 5.2.4
Interim mitigation

Upgrade Plone to version 5.2.4 or later which contains the security patch. If immediate upgrade is not possible, restrict network access to the Plone server and disable or sandbox the lxml parser's external entity resolution capabilities.

Fix this in Plone Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA4.0 h
40.0 hours of engineering $7,000
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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-2021-33511 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