GHSA-944x-pm95-3jpr: Ghost: File Upload Content-Type Spoofing
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 security@ghost.org.
Details
Original advisory: https://github.com/advisories/GHSA-944x-pm95-3jpr
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-539480.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-53948 | coverage & exploitation status | NVD · CVE.org |
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