CVE-2026-66062: SvelteKit: ReDoS (O(n^2)) in content negotiation — unauthenticated DoS via the Accept header
Impact SvelteKit is vulnerable to remote CPU-exhaustion DoS attacks via specifically-crafted Accept headers. The impact is mitigated by default header length limits on most platforms, but in the case of raised or absent limits a denial of service is possible.
Patches The vulnerability is patched in @sveltejs/kit version 2.70.2.
Other sources
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.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/@sveltejs/kitto a version that resolves this vulnerability.Fixed in 2.70.2 - Upgrade
Upgrade
@sveltejs/kitto a version that resolves this vulnerability.Fixed in 2.70.2
Event History
Frequently Asked Questions
What is the severity of CVE-2026-66062?
The severity of CVE-2026-66062 is rated as medium with a score of 5.3.
What impact does CVE-2026-66062 have?
CVE-2026-66062 allows for remote CPU-exhaustion Denial of Service (DoS) attacks through specially-crafted Accept headers.
How can I mitigate CVE-2026-66062?
Mitigation for CVE-2026-66062 involves ensuring that default header length limits are enforced on your platform.
How do I fix CVE-2026-66062?
To fix CVE-2026-66062, update to the latest version of npm/@sveltejs/kit that includes the security patch.
Is CVE-2026-66062 a serious vulnerability?
CVE-2026-66062 is considered a medium-risk vulnerability, but it can lead to denial of service if header limits are raised or absent.