Improper handling of exceptional conditions in Valibot - CVE-2026-59952
Published: July 9, 2026
Vulnerability identifier: #VU137281
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-59952
CWE-ID: CWE-755
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper handling of exceptional conditions in the flatten() helper when processing validation issues containing attacker-controlled object keys that collide with inherited Object.prototype property names. A remote attacker can supply a crafted JSON object that causes record() validation to produce an issue path such as toString and trigger a TypeError in flatten() to cause a denial of service.
This issue is reachable through normal record() validation and affects applications that flatten validation errors for API responses.
Affected software
Valibot
How to mitigate CVE-2026-59952
Install security update from vendor's website.
Valibot - update to 1.4.2