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CVE-2026-42599— Cross-site scripting via spread attributes in Svelte SSR

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 5.55.7之前版本存在跨站脚本漏洞，该漏洞源于使用扩展语法渲染不受信任数据时事件处理属性被包含在HTML输出中，可能导致恶意事件处理注入。

AI Predicted 6.1 Difficulty: Moderate EPSS 0.24% · P13

Possible ATT&CK Techniques 1 AI

T1059 · Command and Scripting Interpreter

Affected Version Matrix 1

VendorProduct Version RangeStatus
sveltejs svelte < 5.55.7 affected
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I. Basic Information for CVE-2026-42599

Vulnerability Information
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Vulnerability Title
Cross-site scripting via spread attributes in Svelte SSR
Source: CVE Program / CVE List V5
Vulnerability Description
Svelte is a performance oriented web framework. Prior to version 5.55.7, when using spread syntax to render attributes from untrusted data, event handler properties are included in the rendered HTML output. If an application spreads user-controlled or external data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers. Note that this vulnerability only triggers if the user's browser has JavaScript enabled but Svelte's hydration mechanism does not reach the vulnerable element before the event fires. This issue has been patched in version 5.55.7.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/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 5.55.7之前版本存在跨站脚本漏洞，该漏洞源于使用扩展语法渲染不受信任数据时事件处理属性被包含在HTML输出中，可能导致恶意事件处理注入。
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 < 5.55.7 -

II. Public POCs for CVE-2026-42599

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III. Intelligence Information for CVE-2026-42599

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Vendor Advisories for CVE-2026-42599 (1)

Vendor Pages for CVE-2026-42599 (1)

Same Patch Batch · sveltejs · 2026-06-09 · 4 CVEs total

CVE-2026-42570 7.5 HIGH Svelte devalue: DoS via sparse array deserialization
CVE-2026-42567 Svelte: ReDoS in `<svelte:element>` Tag Validation
CVE-2026-42573 Svelte: XSS via DOM Clobbering of Internal Framework State

IV. Related Vulnerabilities

Same product: svelte
Same vendor: sveltejs
Same weakness: CWE-79

V. Comments for CVE-2026-42599

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