CVE-2026-27125

Received Received - Intake

Prototype Pollution Exposure via Attribute Spreading in Svelte SSR

Publication date: 2026-02-20

Last updated on: 2026-02-23

Assigner: GitHub, Inc.

Description

svelte performance oriented web framework. Prior to 5.51.5, in server-side rendering, attribute spreading on elements (e.g. <div {...attrs}>) enumerates inherited properties from the object's prototype chain rather than only own properties. In environments where Object.prototype has already been polluted — a precondition outside of Svelte's control — this can cause unexpected attributes to appear in SSR output or cause SSR to throw errors. Client-side rendering is not affected. This vulnerability is fixed in 5.51.5.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-02-20

Last Modified

2026-02-23

Generated

2026-07-06

AI Q&A

2026-02-21

EPSS Evaluated

2026-07-05

NVD

CVE-2026-27125

Affected Vendors & Products

Vendor	Product	Version / Range
svelte	svelte	to 5.51.5 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-915	The product receives input from an upstream component that specifies multiple attributes, properties, or fields that are to be initialized or updated in an object, but it does not properly control which attributes can be modified.

Attack-Flow Graph

Executive Summary

This vulnerability exists in the Svelte web framework prior to version 5.51.5 during server-side rendering (SSR). When using attribute spreading on elements (e.g., <div {...attrs}>), the framework incorrectly enumerates inherited properties from the object's prototype chain instead of only its own properties.

If the Object.prototype has been polluted (i.e., modified with additional properties), which is outside of Svelte's control, this can cause unexpected attributes to appear in the SSR output or cause SSR to throw errors.

This issue does not affect client-side rendering and was fixed in Svelte version 5.51.5.

Impact Analysis

The vulnerability can lead to unexpected attributes appearing in the server-side rendered HTML output or cause server-side rendering to throw errors.

This may result in incorrect or malformed HTML being sent to clients, potentially affecting the functionality or appearance of web pages.

Additionally, SSR errors could cause server instability or downtime, impacting the availability of the web application.

Compliance Impact

I don't know

Detection Guidance

I don't know

Mitigation Strategies

To mitigate this vulnerability, upgrade the Svelte framework to version 5.51.5 or later, where the issue has been fixed.

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