What is CVE-2026-123566?

CVE-2026-123566 is a high-severity vulnerability in Sveltejs Devalue, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-11-08.

How severe is CVE-2026-123566?

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

Resource exhaustion in Sveltejs Devalue

CVE-2026-123566

Sveltejs devalue before 5.9.3 contains a denial of service vulnerability that allows attackers to cause CPU amplification by supplying sparse arrays to uneval. Attackers who influence sparse values passed to uneval can force synchronous work proportional to the declared array length, blocking the event loop.

Vulnerability class: DoS (Denial of Service)

Published 2026-11-08.

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

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Sveltejs Devalue

Weakness classification (CWE)

CWE-400 — Uncontrolled Resource Consumption

References

GitHub Security Advisory (GHSA-hx4r-w6wj-j8fg) (vendor-advisory)
VulnCheck Advisory: Devalue before 5.9.3 CPU Amplification Denial of Service via uneval (third-party-advisory)

Frequently asked questions

What is CVE-2026-123566?: CVE-2026-123566 is a high-severity vulnerability in Sveltejs Devalue, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-11-08.
How severe is CVE-2026-123566?: High severity. CVSS v3 base score is 7.5 out of 10.