CVE-2026-123568 PUBLISHED

Sveltejs devalue before 5.6.3 Prototype Pollution via uneval Output

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

Sveltejs devalue before 5.6.3 contains a prototype pollution vulnerability that allows attackers to alter object prototypes by supplying untrusted data to uneval. When the generated code is later evaluated, it creates objects with polluted prototypes, producing output data whose shape differs from the original input.

CVSS Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
CVSS Score: 2.1

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

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:L/I:L/A:N
CVSS Score: 4.4

Attack Vector	Network	Scope	Changed
Attack Complexity	High	Confidentiality Impact	Low
Privileges Required	High	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 5.6.3 (excl.) Version 5.6.3 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