Input validation error in Fastjson - CVE-2026-16723
Published: July 31, 2026 / Updated: October 2, 2026
Vulnerability identifier: #VU140629
CSH Severity: Critical
CVSS v4: 9.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-16723
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
The vulnerability is being exploited in the wild
Vulnerability details
The vulnerability allows a remote attacker to execute arbitrary code.
The vulnerability exists due to improper input validation in fastjson type resolution logic when parsing user-supplied JSON input. A remote attacker can send a specially crafted JSON payload to execute arbitrary code.
Exploitation requires the application to run as a Spring Boot executable fat-jar under the default configuration with AutoType disabled and SafeMode disabled.
Affected software
Fastjson
How to mitigate CVE-2026-16723
Install security update from vendor's website.
Fastjson - update to 1.2.84