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Unrestricted File UploadWeakness · CWE-434

CVE-2026-53948

MEDIUM · 5.4 CVSS v3.1 Published 2026-06-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable 8 weeks old

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
Ghost is a Node.js content management system. From 6.19.4 until 6.21.1, insufficient validation of the client-supplied Content-Type on Ghost's Admin API file upload endpoint allowed uploaded files to be served from the site with an attacker-chosen content type on S3/GCS storage backends. On installations that serve uploaded files from the same origin as the site, this could have been used to facilitate stored cross-site scripting against site visitors or staff. This vulnerability is fixed in 6.21.1.

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

Ghost's Admin API file upload endpoint insufficiently validated the client-supplied Content-Type header, allowing attackers to upload files with arbitrary MIME types. When storage backends (S3/GCS) serve these files with attacker-controlled content types, and when files are served from the same origin as the site, this enables stored XSS against visitors or staff.

MitigationUpgrade Ghost to version 6.21.1 or later, which contains the fix for proper Content-Type validation on file uploads.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
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 checks

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

  1. Determine Ghost installation version
    Run 'ghost version' in the Ghost installation directory, or check the 'package.json' file for the 'version' field, or access /ghost/api/admin/settings/ via the API and look for the 'version' in the response.
    Affected if The installed version is lower than 6.21.1 and the Admin API file upload endpoint is accessible.
  2. Verify Admin API file upload endpoint exists
    Check if the Ghost Admin API is reachable at /ghost/api/admin/ and confirm file upload routes exist by reviewing API documentation or attempting a request to upload endpoints with appropriate admin authentication.
    Affected if The Admin API is exposed and file upload functionality is enabled.
  3. Identify storage backend configuration
    Inspect the Ghost config file (config.development.json or config.production.json) for the 'storage' setting. Check if it uses 'local-file-storage' or a cloud provider (S3, GCS) by examining the 'active' field under the storage configuration.
    Affected if The storage backend is set to a cloud provider (S3/GCS) or any backend that serves uploaded files with client-supplied Content-Type headers.
  4. Check file serving origin configuration
    Examine the Ghost config file for the 'url' setting (site URL) and compare it to the storage backend's public URL. Verify if uploaded files are served from the same domain as the main site by checking the 'public' URL in storage config or testing a file upload URL.
    Affected if Uploaded files are served from the same origin domain as the Ghost site (same base URL).

A user is affected if their Ghost installation is version lower than 6.21.1, has the Admin API with file upload enabled, uses a storage backend that preserves client-supplied Content-Type headers, and serves uploaded files from the same origin as the site.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Ghost to version 6.21.1 or later, which contains the fix for proper Content-Type validation on file uploads.

Recommended fix High confidence

6.21.1

  1. Backup your Ghost installation and database before upgrading
  2. Upgrade Ghost to version 6.21.1 using your installation method (npm or Docker)
  3. If using npm: run `ghost update` or manually update the version in package.json then run `npm install`
  4. If using Docker: pull the updated Docker image with version 6.21.1
  5. After upgrade, verify the Content-Type header is now properly validated on file uploads
  6. Confirm the site functions correctly after the upgrade

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

Have this fixed 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-2026-53948 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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