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CVE-2026-40074 Svelte CVE debrief

CVE-2026-40074 is a vulnerability in SvelteKit, a framework for rapidly developing robust, performant web applications using Svelte. Prior to version 2.57.1, the redirect function, when called from inside the handle server hook with a location parameter containing characters that are invalid in an HTTP header, will cause an unhandled TypeError. This could result in a denial of service (DoS) on some platforms, especially if the location passed to redirect contains unsanitized user input.

Vendor
Svelte
Product
Kit
CVSS
MEDIUM 6.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-10
Original CVE updated
2026-10-26
Advisory published
2026-04-10
Advisory updated
2026-10-26

Who should care

Web application developers using SvelteKit should assess their exposure and verify if their current version is vulnerable. Defenders should prioritize upgrading to SvelteKit version 2.57.1 or later to prevent potential DoS attacks.

Why it matters

CVE-2026-40074 is a vulnerability in SvelteKit that could lead to a denial of service (DoS) on some platforms. Defenders should prioritize upgrading to SvelteKit version 2.57.1 or later to prevent potential DoS attacks. Web application developers using SvelteKit should assess their exposure and verify if their current version is vulnerable.

  • Potential denial of service (DoS) on some platforms
  • Need to verify if current version is vulnerable
  • Need to upgrade to SvelteKit version 2.57.1 or later

Technical summary

The SvelteKit framework, prior to version 2.57.1, is vulnerable to an unhandled TypeError when the redirect function is called from inside the handle server hook with a location parameter containing characters that are invalid in an HTTP header. This could lead to a denial of service (DoS) on some platforms. The vulnerability is described in the CVE record and NVD vulnerability detail page. The fix is available in SvelteKit version 2.57.1. However, the exact scope of affected versions and potential impact require verification from official sources. Web application developers using SvelteKit should assess their exposure and verify if their current version is vulnerable.

Defensive priority

Defenders should prioritize upgrading to SvelteKit version 2.57.1 or later to prevent potential DoS attacks. Web application developers using SvelteKit should assess their exposure and verify if their current version is vulnerable.

Recommended defensive actions

  • Upgrade to SvelteKit version 2.57.1 or later
  • Assess exposure and verify if current version is vulnerable
  • Monitor for potential DoS attacks
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability is described in the CVE record and NVD vulnerability detail page. The fix is available in SvelteKit version 2.57.1. However, the exact scope of affected versions and potential impact require verification from official sources.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-40074 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-40074

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-40074 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-40074

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.