CVE-2021-33512
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 · uneditedPlone through 5.2.4 allows stored XSS attacks (by a Contributor) by uploading an SVG or HTML document.
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 confidenceStored XSS vulnerability in Plone CMS versions up to 5.2.4 where users with Contributor role can upload malicious SVG or HTML files containing JavaScript that executes when other users view or access these uploaded files.
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<= 5.2.4CVSS 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
- Low
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/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 installed Plone versionCheck the Plone version by logging into the ZMI (Zope Management Interface) at /manage, navigating to the root folder, or checking the versions.ini / plone.app.upgrade log filesAffected if Installed version is 5.2.4 or lower (any version up to and including 5.2.4)
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Verify Contributor role permissionsIn Plone, go to Site Setup > Users and Groups > select a Contributor user, or check the role definition in the ZMI under acl_users > portal_role_managerAffected if Contributor role exists and has permissions to add content
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Confirm file upload capability for ContributorsNavigate to Site Setup > Types > check the content types enabled for Contributors, or in the ZMI check portal_types for allowed content types under Contributor roleAffected if Contributor role can add File or Image content types
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Check if SVG/HTML are permitted upload typesIn Site Settings > Filtering, examine allowed file extensions, or in ZMI check portal_transforms safe_format and mime-type registrations for image/svg+xml and text/htmlAffected if SVG (.svg) or HTML (.html, .htm) file extensions are allowed in upload settings
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Inspect Content Security Policy headersCheck web server or Plone response headers for CSP configuration (if deployed behind Apache/Nginx, check those configs; in Plone check zope.conf or the CSP product if installed)Affected if No CSP headers are set, or CSP allows unsafe-inline scripts
Environment is affected if Plone version is 5.2.4 or lower AND Contributor role can upload SVG or HTML files that are served without sanitization.
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.
From vendor dataRestrict or disable HTML/SVG file uploads for Contributor role, implement server-side content sanitization and Content Security Policy headers, or upgrade to patched Plone version.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 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 $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-33512 — 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-2021-33512 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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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.
- 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