Medium 5.3Published Aug 7, 2026

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

Updated under an hour ago (2026-10-19 10:20 UTC)

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It affects sveltejs kit. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE): CWE-1333
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Aug 7, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

sveltejs kit sveltejs:kit (from the name)	before 2.70.2	CNA record

References

https://github.com/sveltejs/kit/security/advisories/GHSA-29g2-3rmr-qm68x-refsource-confirm
https://github.com/sveltejs/kit/commit/82712fc02c24b1dcf5b25d7a52129cd8455f04f5x-refsource-misc
https://github.com/sveltejs/kit/releases/tag/@sveltejs/kit@2.70.2x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.