DOM XSS in Theme Preview
Impact
An unused endpoint added during the development of 4.0.0 has left sites vulnerable to untrusted users gaining access to Ghost Admin. Attackers can gain access by getting logged in users to click a link containing malicious code. Users do not need to enter credentials and may not know they've visited a malicious site.
Ghost(Pro) has already been patched. We can find no evidence that the issue was exploited on Ghost(Pro) prior to the patch being added.
Self-hosters are impacted if running Ghost a version between 4.0.0 and 4.3.2. Immediate action should be taken to secure your site - see patches & workarounds below.
Patches
Fixed in 4.3.3, all 4.x sites should upgrade as soon as possible. As the endpoint is unused, the patch simply removes it.
Workarounds
- Log out of Ghost Admin
- Suspend any users who cannot log out
- Block access to
/ghost/preview
Example of how to block access in nginx:
location ~ /ghost/preview {
rewrite ^(\/(.*\/)?ghost\/)(.*)$ $1 redirect;
}This redirects the endpoint to /ghost/, which mimics the behaviour after the patch is applied.
References
For more information
If you have any questions or comments about this advisory:
- email us at security@ghost.org
Credits: Paul Gerste, SonarSource (https://www.sonarsource.com/)
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | ghost | >= 4.0.0, < 4.3.3 | 4.3.3 |
References
- https://github.com/TryGhost/Ghost/security/advisories/GHSA-9fgx-q25h-jxrg
- https://nvd.nist.gov/vuln/detail/CVE-2021-29484
- https://github.com/TryGhost/Ghost/commit/14b3431de12e674a0bd562e9230e2891b6903ae2
- https://blog.sonarsource.com/ghost-admin-takeover
- https://forum.ghost.org/t/critical-security-update-available-for-ghost-4-x/22290
- https://github.com/TryGhost/Ghost
- https://security.netapp.com/advisory/ntap-20210618-0006
- https://www.npmjs.com/package/ghost
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N- Weakness (CWE)
CWE-79- Platform
- npm
- Package
ghost- Disclosed
- 29.04.2021
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9fgx-q25h-jxrg - CC BY 4.0
Vulnerability history: ghost
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 61
- First → latest
- 04.2021 10.2026
- Without a fix
- 3
- Exploited in attacks
- 0
Severity breakdown
- Critical 4
- High 16
- Medium 38
- Low 3
Disclosures per year
- 2021: 5
- 2022: 4
- 2023: 3
- 2024: 3
- 2025: 1
- 2026: 45
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