CVE-2026-55660: TinaCMS Cross-Site Scripting Vulnerability

HIGH
Advisory Identifier: GHSA-g5qx-h5f3-mp2f
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CWE-940 CWE-601 CWE-79 CWE-346
Published
Advisory Summary

CVE-2026-55660 is a HIGH cross-site scripting vulnerability (CWE-940: Improper Verification of Source of a Communication Channel) affecting TinaCMS libraries in the npm ecosystem. The issue involves cross-origin postmessage handlers and rich-text url-sanitization bypass enable stored xss and session takeover. Remediation is available by upgrading affected packages to version 3.9.3, 2.5.6.

CVE-2026-55660 at a Glance

CVE Identifier CVE-2026-55660
GHSA Identifier GHSA-g5qx-h5f3-mp2f
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-940: Improper Verification of Source of a Communication Channel
Affected Product TinaCMS
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-55660

To remediate this vulnerability, upgrade all affected TinaCMS dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

tinacms fixed: 3.9.3 
npm install tinacms@3.9.3
@tinacms/app fixed: 2.5.6 
npm install @tinacms/app@2.5.6
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls tinacms

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-55660, inspect your project dependencies using npm:

npm ls tinacms

Analyze the terminal output to locate any version of TinaCMS in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.9.3), your application is affected.

Note: The npm ls tinacms command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-940: Improper Verification of Source of a Communication Channel, where the product establishes a communication channel to handle an incoming request that has been initiated by an actor, but it does not properly verify that the request is coming from the expected origin. In TinaCMS, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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](https://github.com/tinacms/tinacms/pull/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.

CVE-2026-55660 Affected TinaCMS Versions

2 component(s)
Fixed Versions:
3.9.32.5.6
Product / Package Ecosystem Affected Versions Fixed Version
tinacms
npm/tinacms
npm
< 3.9.3
3.9.3
@tinacms/app
npm/@tinacms/app
npm
< 2.5.6
2.5.6

References

GitHub Advisory / Wiki ADVISORY
https://github.com/tinacms/tinacms/security/advisories/GHSA-g5qx-h5f3-mp2f
TinaCMS Source Repository REPOSITORY
https://github.com/tinacms/tinacms/pull/7056
TinaCMS Source Repository REPOSITORY
https://github.com/tinacms/tinacms

Frequently Asked Questions

What is CVE-2026-55660?
CVE-2026-55660 is a security vulnerability in TinaCMS involving Cross-origin postMessage handlers and rich-text URL-sanitization bypass enable stored XSS and session takeover under CWE-940: Improper Verification of Source of a Communication Channel.
Which TinaCMS versions are affected?
Affected versions include releases prior to 3.9.3, 2.5.6 across affected packages: tinacms, @tinacms/app.
What version fixes CVE-2026-55660?
Upgrading to 3.9.3, 2.5.6 (or the latest patched release for your respective branch) resolves the vulnerability.
Is tinacms affected?
Yes, tinacms is affected in releases prior to 3.9.3. Upgrade your dependency to 3.9.3 or later.
Is @tinacms/app affected?
Yes, @tinacms/app is affected in releases prior to 2.5.6. Upgrade your dependency to 2.5.6 or later.
What CWE is associated with CVE-2026-55660?
CVE-2026-55660 is classified under CWE-940: Improper Verification of Source of a Communication Channel (The product establishes a communication channel to handle an incoming request that has been initiated by an actor, but it does not properly verify that the request is coming from the expected origin.).
How can I check npm dependencies for CVE-2026-55660?
Run the dependency tree command: 'npm ls tinacms'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g5qx-h5f3-mp2f",
  "modified" : "2026-06-19T21:15:29Z",
  "published" : "2026-06-19T21:15:29Z",
  "aliases" : [ "CVE-2026-55660" ],
  "summary" : "TinaCMS: Cross-origin postMessage handlers and rich-text URL-sanitization bypass enable stored XSS and session takeover",
  "details" : "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.\n\nFixed in [#7056](https://github.com/tinacms/tinacms/pull/7056) by allow-listing trusted origins and verifying event.source (isFromAdmin, isFromTrustedPreviewOrigin), and by posting only to explicit target origins (never \"*\").\n\nNote: 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "tinacms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.9.3"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@tinacms/app"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.5.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tinacms/tinacms/security/advisories/GHSA-g5qx-h5f3-mp2f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tinacms/tinacms/pull/7056"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tinacms/tinacms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-346", "CWE-601", "CWE-79", "CWE-940" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T21:15:29Z",
    "nvd_published_at" : null
  }
}