XSS in Svelte
CVE-2026-42599
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (13.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 13th percentile — 13.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- Svelte
- Sveltejs Svelte — versions < 5.55.7
Weakness classification (CWE)
References
- github.com/sveltejs/svelte/releases/tag/svelte@5.55.7 (Release Notes)
- github.com/sveltejs/svelte/security/advisories/GHSA-pr6f-5x2q-rwfp (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-42599?
- CVE-2026-42599 is a medium-severity vulnerability in Svelte, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-06-09.
- How severe is CVE-2026-42599?
- Medium severity. CVSS v3 base score is 6.1 out of 10.