---
id: GHSA-53g2-mvcc-q9x3
title: 'Trix: Stored XSS via HTMLParser attribute injection on paste'
summary: 'Trix: Stored XSS via HTMLParser attribute injection on paste'
severity: medium
cvss: 4.6
cwe:
  - CWE-79
vendor: trix
product: trix
ecosystem: npm
affected:
  - trix < 2.1.18
  - action_text-trix < 2.1.18
patched:
  - trix 2.1.18
  - action_text-trix 2.1.18
published: '2026-07-24'
updated: '2026-07-24'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-53g2-mvcc-q9x3'
references:
  - url: 'https://github.com/basecamp/trix/security/advisories/GHSA-53g2-mvcc-q9x3'
  - url: >-
      https://github.com/basecamp/trix/commit/9c0a993d9fc2ffe9d56b013b030bc238f9c0557c
  - url: 'https://github.com/basecamp/trix/releases/tag/v2.1.18'
  - url: 'https://github.com/advisories/GHSA-53g2-mvcc-q9x3'
tags:
  - ghsa
  - npm
ingestedAt: '2026-07-24T16:33:09.516Z'
---

## Overview

### Impact

The Trix editor, in versions prior to 2.1.18, is vulnerable to XSS when crafted HTML is pasted into the editor. The `HTMLParser` processed a mock attachment, a `<span>` carrying an empty `data-trix-attachment="{}"`. The empty attachment object caused the element to bypass attachment handling, so its `data-trix-attributes` were applied to a plain string piece. The pre-2.1.18 `StringPiece.fromJSON` accepted the `href` without validation, so an attacker-supplied `javascript:` URI was carried into the document model and emitted verbatim into the serialized HTML, executing when the content was rendered and clicked.

This is a stored XSS in any application that accepts untrusted rich text through Trix and renders the serialized output to other users. Applications that apply server-side HTML sanitization, such as the Rails built-in sanitizer, are additionally protected because the payload is neutralized on save.

This vulnerability shares its fix with GHSA-53p3-c7vp-4mcc. Both are resolved by the `StringPiece.fromJSON` sanitization added in 2.1.18. This advisory covers the paste and HTMLParser entry vector, while GHSA-53p3-c7vp-4mcc covers the drag-and-drop path through the fallback Level0InputController.

### Patches

Users should upgrade to Trix editor version 2.1.18 or later.

### References

The vulnerability was responsibly reported by HackerOne researcher [newbiefromcoma](https://hackerone.com/newbiefromcoma).

## Affected packages

- `trix < 2.1.18`
- `action_text-trix < 2.1.18`

## Remediation

Upgrade to a patched release:

- `trix 2.1.18`
- `action_text-trix 2.1.18`