Bug 2487076 (CVE-2026-42599)

Summary: CVE-2026-42599 svelte: Svelte: Cross-Site Scripting via untrusted data in spread attributes
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: cdrage, rushinde
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Svelte. When an application uses spread syntax to render attributes from untrusted data, event handler properties are included in the generated HTML output. This allows a remote attacker to inject malicious event handlers that can execute in a victim's web browser, leading to client-side script execution (Cross-Site Scripting). This vulnerability occurs if the user's browser has JavaScript enabled and Svelte's hydration mechanism does not process the affected element before the event is triggered.
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Description OSIDB Bzimport 2026-06-09 18:01:25 UTC 
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.