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CVE-2026-27122— Svelte SSR does not validate dynamic element tag names in `<svelte:element>`

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之前版本存在跨站脚本漏洞，该漏洞源于服务器端渲染期间未验证或清理标签名称，可能导致HTML注入。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.22% · P11

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-27122

Vulnerability Information
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Vulnerability Title
Svelte SSR does not validate dynamic element tag names in `<svelte:element>`
Source: CVE Program / CVE List V5
Vulnerability Description
svelte performance oriented web framework. Prior to 5.51.5, when using <svelte:element this={tag}> in server-side rendering, the provided tag name is not validated or sanitized before being emitted into the HTML output. If the tag string contains unexpected characters, it can result in HTML injection in the SSR output. 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:H/UI:N/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
Svelte 跨站脚本漏洞
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之前版本存在跨站脚本漏洞，该漏洞源于服务器端渲染期间未验证或清理标签名称，可能导致HTML注入。
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-2026-27122

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III. Intelligence Information for CVE-2026-27122

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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-2026-27125 Svelte SSR attribute spreading includes inherited properties from prototype chain
CVE-2026-27118 Cache poisoning in @sveltejs/adapter-vercel
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-79

V. Comments for CVE-2026-27122

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