CVE-2026-55661: Tinacms Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-2vcc-5v34-9jc8
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CWE-87 CWE-79
Published
Advisory Summary

CVE-2026-55661 is a MODERATE cross-site scripting vulnerability (CWE-87: Improper Neutralization of Alternate XSS Syntax) affecting Tinacms libraries in the npm ecosystem. The issue involves tinacms rich-text (slatejson) rendering does not sanitize link/image urls, allowing stored xss via dangerous url schemes. Remediation is available by upgrading affected packages to version 3.9.3, 2.1.7.

CVE-2026-55661 at a Glance

CVE Identifier CVE-2026-55661
GHSA Identifier GHSA-2vcc-5v34-9jc8
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-87: Improper Neutralization of Alternate XSS Syntax
Affected Product Tinacms
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-55661

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/mdx fixed: 2.1.7 
npm install @tinacms/mdx@2.1.7
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-2026-55661, 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-87: Improper Neutralization of Alternate XSS Syntax, where the product does not neutralize or incorrectly neutralizes user-controlled input for alternate script syntax. 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 rich-text parsing and the default link/image renderers did not sanitize the `url` field on Slate link/image nodes. Content containing `javascript:` or `data:text/html` URLs — including case-variant, whitespace-padded, and control-character-obfuscated forms — is rendered into `href`/`src` and executes when the content is viewed. Any actor able to author rich-text content (for example a lower-privileged editor, or imported/external content) can achieve stored XSS against editors and site viewers. Fixed in https://github.com/tinacms/tinacms/pull/7056 via a `sanitizeUrl()` helper (case-insensitive, whitespace/control-character-normalized scheme allow-list) applied recursively to Slate trees at parse time and in the default rich-text rendering.

CVE-2026-55661 Affected Tinacms Versions

2 component(s)
Fixed Versions:
3.9.32.1.7
Product / Package Ecosystem Affected Versions Fixed Version
tinacms
npm/tinacms
npm
< 3.9.3
3.9.3
@tinacms/mdx
npm/@tinacms/mdx
npm
< 2.1.7
2.1.7

References

GitHub Advisory / Wiki ADVISORY
https://github.com/tinacms/tinacms/security/advisories/GHSA-2vcc-5v34-9jc8
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-2026-55661?
CVE-2026-55661 is a security vulnerability in Tinacms involving TinaCMS rich-text (slatejson) rendering does not sanitize link/image URLs, allowing stored XSS via dangerous URL schemes under CWE-87: Improper Neutralization of Alternate XSS Syntax.
Which Tinacms versions are affected?
Affected versions include releases prior to 3.9.3, 2.1.7 across affected packages: tinacms, @tinacms/mdx.
What version fixes CVE-2026-55661?
Upgrading to 3.9.3, 2.1.7 (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/mdx affected?
Yes, @tinacms/mdx is affected in releases prior to 2.1.7. Upgrade your dependency to 2.1.7 or later.
What CWE is associated with CVE-2026-55661?
CVE-2026-55661 is classified under CWE-87: Improper Neutralization of Alternate XSS Syntax (The product does not neutralize or incorrectly neutralizes user-controlled input for alternate script syntax.).
How can I check npm dependencies for CVE-2026-55661?
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-2vcc-5v34-9jc8",
  "modified" : "2026-06-18T13:07:05Z",
  "published" : "2026-06-18T13:07:05Z",
  "aliases" : [ "CVE-2026-55661" ],
  "summary" : "TinaCMS rich-text (slatejson) rendering does not sanitize link/image URLs, allowing stored XSS via dangerous URL schemes",
  "details" : "TinaCMS rich-text parsing and the default link/image renderers did not sanitize the `url` field on Slate link/image nodes. Content containing `javascript:` or `data:text/html` URLs — including case-variant, whitespace-padded, and control-character-obfuscated forms — is rendered into `href`/`src` and executes when the content is viewed. Any actor able to author rich-text content (for example a lower-privileged editor, or imported/external content) can achieve stored XSS against editors and site viewers.\n\nFixed in https://github.com/tinacms/tinacms/pull/7056 via a `sanitizeUrl()` helper (case-insensitive, whitespace/control-character-normalized scheme allow-list) applied recursively to Slate trees at parse time and in the default rich-text rendering.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "tinacms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.9.3"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@tinacms/mdx"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.1.7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/tinacms/tinacms/security/advisories/GHSA-2vcc-5v34-9jc8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/tinacms/tinacms/pull/7056"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/tinacms/tinacms"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79", "CWE-87" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-18T13:07:05Z",
    "nvd_published_at" : null
  }
}