# CVE-2026-42573: Svelte DOM clobbering leading to XSS in internal framework state

Source: https://junglewise.ai/threats/cve-2026-42573-svelte-dom-clobbering-leading-to-xss-in-internal-framework-state  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-09. Updated: 2026-06-09  
License: CC BY 4.0 with a link back

CVE-2026-42573 · Severity: medium · CVSS 4 · Published 2026-06-09

Svelte is a popular web framework used to build user interfaces. A vulnerability exists where an attacker can manipulate the internal state of a web page by providing malicious input to forms that use specific coding patterns. This could allow an attacker to execute unauthorized scripts in a user's browser, potentially leading to the theft of sensitive information or session hijacking.

Technologies: [svelte (npm)](https://junglewise.ai/threats/technologies/svelte). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-42573 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42573 being exploited in the wild.

**How severe is CVE-2026-42573?** Medium severity, with a CVSS score of 4, published 9 June 2026.

**Which products and versions are affected?** svelte (npm) <= 5.55.6, SEMVER:introduced=0,fixed=5.55.7.

**Is there a fix for CVE-2026-42573?** Yes. svelte (npm): upgrade to 5.55.7 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42573 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42573?** Check whether you run svelte (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- svelte (npm): upgrade to 5.55.7 or later

  ```sh
  npm install svelte@5.55.7
  ```


## Technical details

Svelte is vulnerable to DOM Clobbering of its internal framework state, which can be escalated to Cross-Site Scripting (XSS). The vulnerability occurs when a developer uses attribute spreading ({...spread}) on a <form> element while simultaneously using attribute spreading or dynamic 'name' attributes on child <input> or <button> elements. If both the form attributes and the child element names are user-controllable, an attacker can 'clobber' internal properties that Svelte uses to manage the DOM. This allows for the injection of malicious scripts. The issue is fixed in Svelte version 5.55.7.

## Affected products

- sveltejs svelte <= 5.55.6

## Identifiers

- CVE-2026-42573
- GHSA-rcqx-6q8c-2c42

## Timeline

- 2026-05-14: disclosed
- 2026-05-14: advisory
- 2026-05-14: patched: Fixed in version 5.55.7

## References

- [https://api.github.com/users/elliott-with-the-longest-name-on-github](https://api.github.com/users/elliott-with-the-longest-name-on-github)
- [https://github.com/elliott-with-the-longest-name-on-github](https://github.com/elliott-with-the-longest-name-on-github)
- [https://api.github.com/users/elliott-with-the-longest-name-on-github/gists%7B/gist_id%7D](https://api.github.com/users/elliott-with-the-longest-name-on-github/gists%7B/gist_id%7D)
- [https://api.github.com/users/elliott-with-the-longest-name-on-github/repos](https://api.github.com/users/elliott-with-the-longest-name-on-github/repos)
- [https://avatars.githubusercontent.com/u/76245373?v=4](https://avatars.githubusercontent.com/u/76245373?v=4)
- [https://api.github.com/users/elliott-with-the-longest-name-on-github/events%7B/privacy%7D](https://api.github.com/users/elliott-with-the-longest-name-on-github/events%7B/privacy%7D)

## Related threats

- [Svelte XSS via spread attributes in SSR](https://junglewise.ai/threats/cve-2026-42599-svelte-xss-via-spread-attributes-in-ssr)
- [Svelte ReDoS in svelte:element tag validation](https://junglewise.ai/threats/cve-2026-42567-svelte-redos-in-svelte-element-tag-validation)
- [Svelte XSS via insecure promise serialization in hydratable](https://junglewise.ai/threats/svelte-xss-via-insecure-promise-serialization-in-hydratable-3f504409)
- [Svelte XSS via HTML comment injection in SSR error boundary](https://junglewise.ai/threats/cve-2026-27902-svelte-xss-via-html-comment-injection-in-ssr-error-boundary)
- [Svelte XSS in SSR with contenteditable bind:innerText and bind:textContent](https://junglewise.ai/threats/cve-2026-27901-svelte-xss-in-ssr-with-contenteditable-bind-innertext-and-bind)