Vulnerability · Published Jun 9, 2026 · Assigned by GitHub_M

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

Medium 5.1

In plain English

A medium-severity cross-site scripting in svelte from sveltejs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)5.1Medium

Exploit odds (30 days)0.2%top 89.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	svelte	5.55.7	GHSA-pr6f-5x2q-rwfp

Affected products (as reported)

Vendor	Product	Versions
sveltejs	svelte	< 5.55.7

Weakness: CWE-79 · 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

References

https://github.com/sveltejs/svelte/security/advisories/GHSA-pr6f-5x2q-rwfp x_refsource_CONFIRM
https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7 x_refsource_MISC