Summary
TinaCMS: Cross-origin postMessage handlers and rich-text URL-sanitization bypass enable stored XSS and session takeover
TinaCMS 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. 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.
Fixed in #7056 by allow-listing trusted origins and verifying event.source (isFromAdmin, isFromTrustedPreviewOrigin), and by posting only to explicit target origins (never "*").
Note: the rich-text URL-sanitization issue previously bundled here has been split into its own advisory (GHSA-2vcc-5v34-9jc8) so each vulnerability can receive a distinct CVE.
Impact
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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tinacms to 3.9.3 or later; @tinacms/app to 2.5.6 or later
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Frequently Asked Questions
- What is CVE-2026-55660? CVE-2026-55660 is a high-severity cross-site scripting (XSS) vulnerability in tinacms (npm), affecting versions < 3.9.3. It is fixed in 3.9.3, 2.5.6. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- Which packages are affected by CVE-2026-55660?
tinacms(npm) (versions < 3.9.3)@tinacms/app(npm) (versions < 2.5.6)
- Is there a fix for CVE-2026-55660? Yes. CVE-2026-55660 is fixed in 3.9.3, 2.5.6. Upgrade to this version or later.
- Is CVE-2026-55660 exploitable, and should I be worried? Whether CVE-2026-55660 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-55660 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-55660?
- Upgrade
tinacmsto 3.9.3 or later - Upgrade
@tinacms/appto 2.5.6 or later
- Upgrade