Critical Fastjson Zero-Day CVE-2026-16723 Actively Exploited for Remote Code Execution on Java Servers
A critical zero-day vulnerability tracked as CVE-2026-16723 is being actively exploited in Fastjson 1.x versions ranging from 1.2.68 to 1.2.83. The flaw enables unauthenticated remote code execution on Java servers that process attacker-controlled JSON, particularly when applications run as Spring Boot executable fat JARs. Exploitation succeeds even when AutoType is disabled and does not require elevated privileges or user interaction. No official patch is available for the 1.x branch, forcing organizations to rely on SafeMode activation or migration to fastjson2. Active campaigns have primarily targeted organizations in the United States, with additional activity observed in Singapore and Canada across finance, healthcare, and retail sectors. The vulnerability stems from type resolution logic that allows attackers to bypass restrictions via resource lookups before security controls are applied.
HispasecJul 28, 2026Translated from Spanish