CVE-2026-42599 MEDIUM

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

Vendor Sveltejs
Product svelte
Weakness CWE-79 · XSS
Published June 9, 2026
Last update June 9, 2026

CVSS base score

5.1/10
Attack vector Network
Attack complexity High
Privileges required High
User interaction None
Confidentiality
Integrity

CVSS vector

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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

June 9, 2026 CVE published
June 9, 2026 Record updated

Related vulnerabilities

04Related CVE