What’s Vulnerable › Vulnerabilities

CVE-2026-66062: SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-07 · updated 2026-10-24
• Weakness: CWE-1333

Description

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.

Affected products

• sveltejs kit: before 2.70.2

References

• https://github.com/sveltejs/kit/commit/82712fc02c24b1dcf5b25d7a52129cd8455f04f5
• https://github.com/sveltejs/kit/releases/tag/@sveltejs/kit@2.70.2
• https://github.com/sveltejs/kit/security/advisories/GHSA-29g2-3rmr-qm68

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