CVE-2026-123561 PUBLISHED

Sveltejs devalue before 5.9.3 proto Rejection Bypass via Property-Key Coercion

Assigner: VulnCheck
Reserved: 06.11.2026 Published: 08.11.2026 Updated: 08.11.2026

devalue before 5.9.3 allows malformed null-prototype object keys to bypass parse's proto rejection through property-key coercion, an incomplete fix for GHSA-mwv9-gp5h-frr4. Attackers can supply crafted payloads that yield objects with a proto own property, which alone does not cause prototype pollution.

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CVSS Score: 6.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	Low	Integrity	None
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 3.7

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	sveltejs
Product	devalue
Versions	Default: unaffected affected from 0 to 5.9.3 (excl.) Version 5.9.3 is unaffected

Credits

elliott-with-the-longest-name-on-github remediation developer

References

Problem Types

Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') CWE