EUVD-2026-39021Severity by source
AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Admin API authentication required (PR:L); S3/GCS same-origin serving is deployment-specific but not complexity-raising for an authenticated attacker; XSS crosses browser origin boundary (S:C, UI:R); no availability impact applies.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Stored cross-site scripting in Ghost CMS (versions 6.19.4 through 6.21.0) is enabled by the Admin API file upload endpoint accepting and preserving attacker-supplied Content-Type headers without server-side validation. When Ghost is configured with S3 or GCS storage backends that serve uploaded files from the same origin as the site, an authenticated attacker can upload a file with a crafted Content-Type (e.g., text/html) that causes browsers to execute it as HTML or JavaScript, enabling stored XSS against visitors and staff. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Authenticated access to the Ghost Admin API is required - the CVSS vector PR:L confirms a low-privileged authenticated account is the minimum prerequisite, not unauthenticated access. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 score of 5.4 (Medium) with vector AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N accurately captures the risk profile. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An authenticated attacker with Ghost Admin API access (e.g., a contributor or staff account) uploads an HTML file with the Content-Type header manually set to text/html via a crafted multipart POST request to the upload endpoint. The file is stored on the S3 or GCS backend with that MIME type. … |
| Remediation | Upgrade Ghost to version 6.21.1, which introduces server-side enforcement of acceptable Content-Type values on the Admin API upload endpoint. … Detailed patch versions, workarounds, and compensating controls in full report. |
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