CVE-2026-40073: Svelte SvelteKit body size limit bypass in adapter-node

CVE-2026-40073 · Severity: high · CVSS 7.5 · Published 2026-04-10

SvelteKit's Node.js adapter includes a request body size limit to protect against large payload attacks, but this protection can be bypassed on chunked HTTP requests. An attacker sending malformed or chunked requests could send payloads larger than the configured limit, potentially leading to denial-of-service or resource exhaustion on the application server. However, size limits enforced by external infrastructure (WAF, CDN, load balancer) remain effective.

Technologies: @sveltejs/kit (npm), Svelte Kit, SvelteKit. Vendors: npm, Svelte.

Quick answers

Is CVE-2026-40073 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-40073 being exploited in the wild.
How severe is CVE-2026-40073?
High severity, with a CVSS score of 7.5, published 10 April 2026.
Which products and versions are affected?
@sveltejs/kit (npm) <= 2.57.0, SEMVER:introduced=0,fixed=2.57.1; Svelte Kit <= 2.57.0; SvelteKit <= 2.57.0.
Is there a fix for CVE-2026-40073?
Yes. @sveltejs/kit (npm): upgrade to 2.57.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-40073 attacked?
It is attacked over the network.
Am I affected by CVE-2026-40073?
Check whether you run @sveltejs/kit (npm), Svelte Kit or SvelteKit at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @sveltejs/kit (npm): upgrade to 2.57.1 or later
    npm install @sveltejs/kit@2.57.1

Technical details

The vulnerability exists in the get_raw_body() function of @sveltejs/adapter-node, which handles HTTP request body parsing. The root cause is improper validation of the BODY_SIZE_LIMIT when processing chunked transfer-encoded requests. Specifically, the code failed to enforce size limits when the Content-Length header was absent and Transfer-Encoding: chunked was used—a legitimate HTTP scenario. The vulnerability requires network access but has low attack complexity; no authentication or user interaction is needed. An attacker can craft HTTP requests with chunked encoding to bypass the body size limit and exhaust application resources. The fix, included in version 2.57.1, adds proper validation to reject oversized requests regardless of the encoding method. A patch is available; upgrade to @sveltejs/kit@2.57.1 or later.

Affected products

  • SvelteJS @sveltejs/kit <= 2.57.0

Identifiers

  • CVE-2026-40073
  • GHSA-2crg-3p73-43xp

Timeline

  • 2026-04-10: disclosed: Published to GitHub Security Advisory
  • 2026-04-09: patched: Fix committed; released in @sveltejs/kit@2.57.1

References

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