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.

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-c…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.002 (6.4th percentile) — read the EPSS interpretation.

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.

Affected products

Svelte
Sveltejs Svelte — versions < 5.55.7

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security-advisories@github.com (x_refsource_MISC, Release Notes)
security-advisories@github.com (x_refsource_CONFIRM, 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.