Vulnerability in Sveltejs Kit
CVE-2026-66062
SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to 2.70.2, the content negotiation header parser used by SvelteKit's request handling (for headers such as Accept) uses a regular expression vulnerable to quadratic backtracking, so a maliciously crafted header value can cause excessive CPU consumption and degrade or deny service. Version 2.70.2 fixes the issue.
Vulnerability class: ReDoS (Regular Expression Denial of Service)
EPSS: 0.003 (21.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
Affected products
- Sveltejs Kit — versions < 2.70.2
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_CONFIRM)
Frequently asked questions
- What is CVE-2026-66062?
- CVE-2026-66062 is a medium-severity vulnerability in Sveltejs Kit, classified under Inefficient Regular Expression Complexity. CVSS score: 5.3/10. Published 2026-08-07.
- How severe is CVE-2026-66062?
- Medium severity. CVSS v3 base score is 5.3 out of 10.