Fastjson 1.x RCE Vulnerability Targeted in Attacks With No Patched Available
Jul 25, 2026
Vulnerability / Application Security
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 Fastjson 1.2.68 through 1.2.83, a Spring Boot executable fat-JAR, a network-reachable path that sends attacker-controlled JSON to an affected parser, and SafeMode left at its disabled default. AutoType can remain disabled, and no classpath gadget is required. As of July 25, Alibaba had not released a fixed Fastjson 1.x version. Organizations that cannot migrate immediately should enable SafeMode with -Dfastjson.parser.safeMode=true or use com.alibaba:fastjson:1.2.83_noneautotype . Alibaba lists migration to Fastjson2 as the long-term fix. Alibaba published its advisory on July 21 follo...