CVE-2021-29484
DOM XSS in Theme Preview
Description
### 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 - [Forum Post](https://forum.ghost.org/t/critical-security-update-available-for-ghost-4-x/22290) ### 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/)
How to fix CVE-2021-29484
To remediate CVE-2021-29484, upgrade the affected package to a fixed version below.
- —upgrade to 4.3.3 or later
- —upgrade to 4.3.3 or later
Is CVE-2021-29484 being exploited?
Likely — EPSS is 57.0%, placing CVE-2021-29484 in the top tier of vulnerabilities by exploitation probability. Prioritise patching.