CVE-2026-53948 is a medium-severity (CVSS 5.4) Unrestricted File Upload vulnerability in ghost. A fix is available for ghost — see the affected versions and patch details below.
Ghost: File Upload Content-Type Spoofing
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53948.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-53948 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 383,485 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
ghostnpmDescription
Impact
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.
Vulnerable versions
This vulnerability is present in Ghost from v6.19.4 up to v6.21.0.
Patches
v6.21.1 contains a fix for this issue.
How to update
For self-hosters using Docker, find Docker's official Ghost image here. Updating a Docker-based Ghost instance is documented here.
If your Ghost is a Ghost-CLI install see our documentation on updating it to the latest version here.
For more information
If you have any questions or comments about this advisory, email us at [email protected].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | ghost | ≥ 6.19.4&&< 6.21.1 | 6.21.1npm install ghost@6.21.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ghost, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ghost to 6.21.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53948 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-53948 in your dependencies?
Find it across npm, including transitive dependencies.