CVE-2026-82259: sveltekit Insecure Deserialization

Description

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0037

Probability of exploitation

0.31%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-502 Deserialization of Untrusted Data

Affected Products

Vendor	Product	Versions
svelte	sveltekit	2.49.0 — 2.53.3

References

Advisories & Patches

https://github.com/sveltejs/kit/security/advisories/GHSA-fpg4-jhqr-589c

Other References

https://www.vulncheck.com/advisories/sveltekit-2.49.0-before-2.53.3-denial-of-service-via-form

Frequently Asked Questions

What is CVE-2026-82259? +

SvelteKit versions from 2.49.0 through 2.53.2 (fixed in 2.53.3) contain a deserialization expansion issue in the experimental form remote function. When an application enables experimental.remoteFunctions and uses the form function to process the files array without validating files.length or individual file sizes, an attacker can submit relatively small inputs that expand into very large file arrays, leading to expensive processing and denial of service. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-82259? +

CVE-2026-82259 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0037, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-82259? +

CVE-2026-82259 affects products from svelte, specifically: sveltekit. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-82259? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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