CVE-2026-73428 Trix: Stored XSS via HTMLParser attribute injection on paste
Attackers can inject malicious JavaScript via crafted HTML pastes in Trix, leading to stored XSS when other users interact with the content.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-73428?
CVE-2026-73428 is a medium-severity cross-site scripting vulnerability in basecamp trix, published on 13 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2026-73428?
4 open source packages ship an affected version, including action_text-trix and trix.
| Package | Affected | Fixed in |
|---|---|---|
action_text-trix RubyGems | All versions | 2.1.18 |
action_text-trix RubyGems | All versions | 2.1.18 |
trix npm | All versions | 2.1.18 |
trix npm | All versions | 2.1.18 |
How do I fix CVE-2026-73428?
Upgrade action_text-trix to 2.1.18 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-73428 being exploited?
There is no known exploitation of CVE-2026-73428 in the wild and no public exploit code.
Sources
Also known as GHSA-53g2-mvcc-q9x3.