Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

Medium severity, with a CVSS score of 4, published 16 January 2026.

Which products and versions are affected?

svelte (npm) SEMVER:introduced=3.0.0,fixed=3.59.2.

Is there a fix for This vulnerability?

Yes. svelte (npm): upgrade to 3.59.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

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.

Svelte XSS in textarea bind:value during server-side rendering

Severity: medium · CVSS 4 · Published 2026-01-16

Svelte is a popular JavaScript framework used to build web applications. When using server-side rendering with a textarea element that binds user-controlled data via bind:value, the framework fails to properly escape the value, allowing an attacker to inject malicious JavaScript code that executes in users' browsers. This can lead to session hijacking, credential theft, or other attacks against site visitors.

Technologies: svelte (npm). Vendors: npm.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: Medium severity, with a CVSS score of 4, published 16 January 2026.
Which products and versions are affected?: svelte (npm) SEMVER:introduced=3.0.0,fixed=3.59.2.
Is there a fix for This vulnerability?: Yes. svelte (npm): upgrade to 3.59.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: 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 3.59.2 or later
```
npm install svelte@3.59.2
```

Technical details

The vulnerability is a cross-site scripting (XSS) flaw in Svelte's server-side rendering (SSR) logic. When a textarea element uses two-way binding (bind:value={...}) with untrusted data, the value is inserted into the HTML output without proper escaping, allowing an attacker to break out of the textarea context and inject arbitrary HTML and JavaScript. The vulnerability requires SSR to be enabled and the textarea's value to be populated from user-controlled input. The flaw was introduced in version 3.0.0 and fixed in version 3.59.2. Attackers can exploit this via network access to applications using affected versions without requiring authentication or special privileges.

Affected products

Svelte Svelte >=3.0.0, <3.59.2

Timeline

2026-01-16: disclosed
2026-01-16: patched: Version 3.59.2 released with fix

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.