5.3

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

Deferred
AliasesGHSA-29g2-3rmr-qm68
Published 07-08-2026Last modified 07-08-2026

Vulnerability summary

CVE-2026-66062 is a medium (CVSS 5.3) vulnerability in sveltejs kit. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 43.3% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 5.3, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.51%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 07-08-2026
    PublishedVulnerability first disclosed.
  2. 07-08-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.51%

Chance of exploitation in the next 30 days

Percentile

43%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.51% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

@sveltejs1 product
  • kit< 2.70.2
Sveltejs1 product

2 vendors · 2 products

References

4 links