What is CVE-2026-30226?

CVE-2026-30226 is a high-severity vulnerability in Svelte Devalue, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 7.5/10. Published 2026-03-11.

How severe is CVE-2026-30226?

High severity. CVSS v3 base score is 7.5 out of 10.

Prototype Pollution in Svelte Devalue

CVE-2026-30226

Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. In devalue v5.6.3 and earlier, devalue.parse and devalue.unflatten were susceptible to prototype pollution via maliciously crafted payloads. Successful exploitation could lead to Denial of Service (DoS) or type confusion. This vulnerability is fixed in 5.6.4.

Vulnerability class: Prototype Pollution

Published 2026-03-11 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.006 (45.1th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002

Affected products

Svelte Devalue
Sveltejs Devalue — versions < 5.6.4

Weakness classification (CWE)

CWE-1321 — Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution)

References

github.com/sveltejs/devalue/security/advisories/GHSA-cfw5-2vxh-hr84 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-30226?: CVE-2026-30226 is a high-severity vulnerability in Svelte Devalue, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 7.5/10. Published 2026-03-11.
How severe is CVE-2026-30226?: High severity. CVSS v3 base score is 7.5 out of 10.