5.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2025-15265

CVE-2025-15265: Svelte 5.46.0 - Hydratable Key Script-Breakout XSS (SSR)

An SSR XSS exists in async hydration when attacker‑controlled keys are passed to hydratable. The key is embedded inside a <script> block without HTML‑safe escaping, allowing </script> to terminate the script and inject arbitrary JavaScript. This enables remote script execution in users' browsers, with potential for session theft and account compromise. This issue affects Svelte: from 5.46.0 before 5.46.3.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2025-15265

CVE-2025-15265:

5.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
svelte	npm	>= 5.46.0, <= 5.46.3	5.46.4

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability exists in the server-side rendering logic of Svelte, specifically in how hydratable data keys are serialized. The Renderer.render function was using JSON.stringify to process these keys before embedding them into a <script> block in the HTML output. However, JSON.stringify does not escape characters such as < and /, which can be used to prematurely close the <script> tag and inject arbitrary HTML and JavaScript. The provided patch replaces the unsafe JSON.stringify call with devalue.uneval. The devalue library is designed to safely serialize JavaScript data, including escaping characters that could lead to XSS vulnerabilities. The test case added in the patch confirms this by using a malicious key containing </script><script>... which would exploit the vulnerability if not for the fix. Therefore, the Renderer.render function is the exact location of the vulnerability.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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