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CVE-2026-27125— Svelte SSR attribute spreading includes inherited properties from prototype chain

Quick assessment

Affected
sveltejs svelte
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Svelte是Svelte开源的一种构建 Web 应用程序的新方法。 Svelte 5.51.5之前版本存在安全漏洞，该漏洞源于服务器端渲染期间属性扩展枚举了继承的属性，可能导致意外属性出现或错误。

AI Predicted 6.5 Difficulty: Moderate EPSS 0.50% · P40

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-27125

Vulnerability Information
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Vulnerability Title
Svelte SSR attribute spreading includes inherited properties from prototype chain
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-915
Source: CVE Program / CVE List V5
Vulnerability Title
Svelte 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Svelte是Svelte开源的一种构建 Web 应用程序的新方法。 Svelte 5.51.5之前版本存在安全漏洞，该漏洞源于服务器端渲染期间属性扩展枚举了继承的属性，可能导致意外属性出现或错误。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
sveltejs svelte < 5.51.5 -

II. Public POCs for CVE-2026-27125

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III. Intelligence Information for CVE-2026-27125

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Same Patch Batch · sveltejs · 2026-02-20 · 5 CVEs total

CVE-2026-27119 Svelte affected by XSS in SSR `<option>` element
CVE-2026-27118 Cache poisoning in @sveltejs/adapter-vercel
CVE-2026-27122 Svelte SSR does not validate dynamic element tag names in `<svelte:element>`
CVE-2026-27121 Svelte affected by cross-site scripting via spread attributes in Svelte SSR

IV. Related Vulnerabilities

Same product: svelte
Same vendor: sveltejs
Same weakness: CWE-915

V. Comments for CVE-2026-27125

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