CVE-2026-42599
Svelte SSR vulnerable to cross-site scripting via spread attributes
Published: 5/14/2026Modified: 5/14/2026
Description
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 is similar to but different from [CVE-2026-27121](https://nvd.nist.gov/vuln/detail/CVE-2026-27121).
Affected packages (1)
- npm/sveltefrom 0, < 5.55.7
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |