CVE-2026-42599
MediumCVSS 6.1Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
Svelte prior to version 5.55.7 contains a vulnerability where, when using spread syntax to render attributes from untrusted data, event handlers are included in the rendered HTML output. If an application spreads user-controlled data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers. The vulnerability only triggers if the user's browser has JavaScript enabled and Svelte's hydration mechanism does not reach the vulnerable element before the event fires.
Risk Assessment
An attacker can inject malicious event handlers, leading to code execution in the victim's browser and potential data theft or session hijacking.
Recommendation
Immediately upgrade Svelte to version 5.55.7 or later.
Other vulnerabilities in Svelte
See all- CVE-2026-42573Medium
Svelte prior to version 5.55.7 is vulnerable to DOM clobbering of its internal framework state on elements, potentially leading to XSS attacks.
- CVE-2026-42567High
Svelte framework versions 5.51.5 through 5.55.6 have a ReDoS vulnerability in <svelte:element this={tag}></svelte:element>. An internal regex can take exponential time to test.
Original NVD description (English source)
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.