Npm · @Tinacms/App · CVE-2026-55660
**Name of the Vulnerable Software and Affected Versions**
@tinacms/app versions prior to 2.5.6
tinacms versions prior to 3.9.3
**Description**
Cross-origin postMessage handlers allow for stored XSS and session takeover. The software registers window message listeners—specifically the useTina overlay handler, the OAuth authentication popup handler, and the admin↔preview iframe GraphQL reducer—that process `event.data` without verifying `event.origin` or `event.source`. Additionally, it posts messages using non-specific target origins. A malicious page visited by a victim, or a window in an opener/iframe relationship with a Tina admin, can forge messages to control the editor, inject preview content, or manipulate the OAuth popup channel to hijack an authenticated editing session.
**Recommendations**
Update @tinacms/app to version 2.5.6.
Update tinacms to version 3.9.3.