CVE-2026-123566— Devalue before 5.9.3 CPU Amplification Denial of Service via uneval

Quick assessment

Affected

sveltejs devalue

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Sveltejs 的 devalue 库在 5.9.3 版本之前存在拒绝服务（DoS）漏洞。攻击者可以通过向函数传递稀疏数组（sparse arrays），引发 CPU 资源放大攻击。若攻击者能够控制传入的稀疏值，即可强制执行与声明的数组长度成正比的同步工作，从而阻塞事件循环。

CVSS 7.5 · High Updated Nov 08, 2026

Possible ATT&CK Techniques 1 AI

T1499.002 · Service Exhaustion Flood

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Vulnerability Information

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Vulnerability Title

Devalue before 5.9.3 CPU Amplification Denial of Service via uneval

Source: CVE Program / CVE List V5

Vulnerability 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.

Source: CVE Program / CVE List V5

CVSS Information

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

Source: CVE Program / CVE List V5

Vulnerability Type

未加控制的资源消耗(资源穷尽)

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
sveltejs	devalue	0 ~ 5.9.3	-

II. Public POCs for CVE-2026-123566

#	POC Description	Source Link	Shenlong Link

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III. Intelligence Information for CVE-2026-123566

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Other References for CVE-2026-123566 (2)

https://github.com/sveltejs/devalue/security/advisories/GHSA-hx4r-w6wj-j8fg vendor-advisory
https://www.vulncheck.com/advisories/devalue-before-5.9.3-cpu-amplification-denial-of-service-via-uneval third-party-advisory

https://www.cve.org/CVERecord?id=CVE-2026-123566

Same Patch Batch · sveltejs · 2026-11-08 · 9 CVEs total

CVE-2026-123564	7.5 HIGH	Sveltejs devalue before 5.9.3 Memory Exhaustion via uneval Sparse Arrays
CVE-2026-123569	7.5 HIGH	Devalue before 5.6.3 Denial of Service via Sparse Array Serialization
CVE-2026-123563	7.5 HIGH	Devalue before 5.9.3 Typed-Array Allocation Validation Bypass via parse
CVE-2026-123562	7.5 HIGH	Devalue 5.8.0 before 5.9.3 Denial of Service via stringifyAsync Unhandled Rejection
CVE-2026-123565	7.5 HIGH	Devalue before 5.9.3 Quadratic Expansion Denial of Service via uneval
CVE-2026-123568	4.4 MEDIUM	Sveltejs devalue before 5.6.3 Prototype Pollution via uneval Output
CVE-2026-123567	3.7 LOW	Sveltejs devalue before 5.6.4 Prototype Injection via parse and unflatten
CVE-2026-123561	3.7 LOW	Sveltejs devalue before 5.9.3 __proto__ Rejection Bypass via Property-Key Coercion

IV. Related Vulnerabilities

Same product: devalue

Same vendor: sveltejs

Same weakness: CWE-400