CVE-2026-123566 Devalue before 5.9.3 CPU Amplification Denial of Service via uneval
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-123566?
CVE-2026-123566 is a high-severity vulnerability in sveltejs devalue, published on 8 Nov 2026.
Official description
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.
Weakness: CWE-400
Which versions are affected by CVE-2026-123566?
1 open source package ship an affected version, including devalue.
| Package | Affected | Fixed in |
|---|---|---|
devalue npm | All versions | 5.9.3 |
How do I fix CVE-2026-123566?
Upgrade devalue to 5.9.3 or later.
Is CVE-2026-123566 being exploited?
There is no known exploitation of CVE-2026-123566 in the wild and no public exploit code.
Sources
Also known as CLSA-2026-1791626697, CLSA-2026-1792230898, CLSA-2026-1792230990, CLSA-2026-1792231253, GHSA-4qxq-46gj-rw38, GHSA-hx4r-w6wj-j8fg.