Fastjson 1.x RCE Vulnerability Targeted in Attacks With No Patched Available

Security firms ThreatBook and Imperva say attackers are targeting a critical flaw in Fastjson, Alibaba’s JSON library for Java. In affected Spring Boot applications, a malicious JSON request can execute code without authentication, with the privileges of the Java process.

Tracked as CVE-2026-16723, the vulnerability carries an Alibaba-assigned CVSS score of 9.0. The confirmed chain requires