CVE-2026-55660 TinaCMS: Cross-origin postMessage handlers and rich-text URL-sanitization bypass enable stored XSS and session takeover
Attackers can exploit unverified postMessage handlers and URL sanitization flaws to inject scripts and hijack authenticated editing sessions in TinaCMS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-55660?
CVE-2026-55660 is a high-severity cross-site scripting vulnerability in @tinacms/app, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Tina is a headless content management system. In versions prior to @tinacms/app 2.5.6 and tinacms 3.9.3, cross-origin postMessage handlers and a rich-text URL-sanitization bypass enable stored XSS and session takeover. The library registers window message listeners — the useTina overlay handler, the OAuth authentication popup handler, and the admin↔preview iframe GraphQL reducer — that act on event.data without verifying event.origin or event.source and post messages using non-specific target origins, while insufficient URL sanitization in rich-text content allows malicious URLs to persist and execute. A page the victim visits (or a window in an opener/iframe relationship with a Tina admin) can forge messages to drive the editor, inject preview content, or observe/forge the OAuth popup channel to take over an authenticated editing session. This issue has been fixed in versions @tinacms/app 2.5.6 and tinacms 3.9.3.
Which versions are affected by CVE-2026-55660?
4 open source packages ship an affected version, including @tinacms/app and tinacms.
| Package | Affected | Fixed in |
|---|---|---|
@tinacms/app npm | All versions | 2.5.6 |
@tinacms/app npm | All versions | 2.5.6 |
tinacms npm | All versions | 3.9.3 |
tinacms npm | All versions | 3.9.3 |
How do I fix CVE-2026-55660?
Upgrade @tinacms/app to 2.5.6 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-55660 being exploited?
There is no known exploitation of CVE-2026-55660 in the wild and no public exploit code.
Sources
Also known as GHSA-g5qx-h5f3-mp2f.