CVE-2026-123567

LOW 3.7

Sveltejs devalue before 5.6.4 Prototype Injection via parse and unflatten

CVSS Score

3.7

EPSS Score

0.0%

EPSS Percentile

0th

Sveltejs devalue before 5.6.4 contains a prototype injection vulnerability that allows attackers to inject __proto__ own properties into objects returned by devalue.parse and devalue.unflatten. Attackers can supply crafted serialized input that, when downstream code merges results via Object.assign, alters the target object's prototype.

CWE	CWE-1321
Vendor	sveltejs
Product	devalue
Published	Nov 8, 2026

Stay Ahead of the Next One

Get instant alerts for sveltejs devalue

Be the first to know when new low vulnerabilities affecting sveltejs devalue are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Affected Versions

sveltejs / devalue

0 < 5.6.4

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/sveltejs/devalue/security/advisories/GHSA-mwv9-gp5h-frr4 vulncheck.com: https://www.vulncheck.com/advisories/sveltejs-devalue-before-5.6.4-prototype-injection-via-parse-and-unflatten

Credits

elliott-with-the-longest-name-on-github KarimPwnz wim-vercel 🔍 mattiasljungstrom