# CVE-2026-82259: SvelteKit deserialization expansion in form remote function

Source: https://junglewise.ai/threats/cve-2026-82259-sveltekit-deserialization-expansion-in-form-remote-function  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-28. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-82259 · Severity: high · CVSS 7.5 · Published 2026-08-28

SvelteKit is a web framework for building fast, interactive applications. When the experimental remote functions feature is enabled, small inputs can be expanded into very large file arrays that cause denial of service if an application processes them without validation. This affects only applications that enable the experimental feature and don't validate file sizes.

Technologies: [@sveltejs/kit (npm)](https://junglewise.ai/threats/technologies/sveltejs-kit), [SvelteKit](https://junglewise.ai/threats/technologies/sveltekit). Vendors: [npm](https://junglewise.ai/threats/vendors/npm), [Svelte](https://junglewise.ai/threats/vendors/svelte).

## Quick answers

**Is CVE-2026-82259 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-82259 being exploited in the wild.

**How severe is CVE-2026-82259?** High severity, with a CVSS score of 7.5, published 28 August 2026.

**Which products and versions are affected?** @sveltejs/kit (npm) SEMVER:introduced=2.49.0,fixed=2.53.3; SvelteKit 2.49.0 to 2.53.2.

**Is there a fix for CVE-2026-82259?** Yes. @sveltejs/kit (npm): upgrade to 2.53.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-82259 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-82259?** Check whether you run @sveltejs/kit (npm) 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 2.53.3 or later

  ```sh
  npm install @sveltejs/kit@2.53.3
  ```


## Technical details

The vulnerability is a deserialization expansion issue (CWE-770) in SvelteKit's experimental `form` remote function. An attacker can craft relatively small inputs that deserialize into very large file arrays. The attack requires network access and only affects applications with `experimental.remoteFunctions: true` enabled and processing file arrays without length or size validation. An attacker can trigger expensive processing on oversized data structures, resulting in denial of service. The issue is fixed in version 2.53.3 by preventing overlapping file metadata during deserialization.

## Affected products

- Svelte SvelteKit 2.49.0 to 2.53.2

## Identifiers

- CVE-2026-82259
- GHSA-fpg4-jhqr-589c

## Timeline

- 2026-02-28: disclosed: Advisory published
- 2026-02-28: patched: Fixed in version 2.53.3

## References

- [https://github.com/sveltejs/kit/security/advisories/GHSA-fpg4-jhqr-589c](https://github.com/sveltejs/kit/security/advisories/GHSA-fpg4-jhqr-589c)
- [https://github.com/sveltejs/kit/commit/faba869db3644077169bf5d7c6e41fd5f3d6c65e](https://github.com/sveltejs/kit/commit/faba869db3644077169bf5d7c6e41fd5f3d6c65e)

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