CVE-2026-123567— Sveltejs devalue before 5.6.4 Prototype Injection via parse and unflatten

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 5.6.4 版本之前存在原型注入漏洞。该漏洞允许攻击者向由和返回的对象中注入自有属性。攻击者可提供精心构造的序列化输入；当下游代码通过合并结果时，该输入会修改目标对象的原型。

CVSS 3.7 · Low Updated Nov 08, 2026

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

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Vulnerability Information

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Vulnerability Title

Sveltejs devalue before 5.6.4 Prototype Injection via parse and unflatten

Source: CVE Program / CVE List V5

Vulnerability Description

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.

Source: CVE Program / CVE List V5

CVSS Information

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

Source: CVE Program / CVE List V5

Vulnerability Type

CWE-1321

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
sveltejs	devalue	0 ~ 5.6.4	-

II. Public POCs for CVE-2026-123567

#	POC Description	Source Link	Shenlong Link

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III. Intelligence Information for CVE-2026-123567

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Other References for CVE-2026-123567 (2)

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

https://www.cve.org/CVERecord?id=CVE-2026-123567

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-2026-123566	7.5 HIGH	Devalue before 5.9.3 CPU Amplification Denial of Service via uneval
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-2026-123561	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-1321