FastJSON @JSONType RCE Lab: public exploit bypasses autoType=OFF

Tue, 21 Jul 2026 12:43:35 +0000

Engineer — Act: A public Docker lab with a working one-payload exploit now exists for fastjson 1.2.66–1.2.83; critically, autoType=OFF and parseObject binding are not effective mitigations. Audit your dependency tree for fastjson in this range and upgrade to 1.2.84+ (or fastjson2), treating autoType-disabled deployments as unprotected.
SOC/IR — Plan: The public exploit lab lowers the bar for threat actors to weaponize this Spring Boot class-loading RCE chain. Build or tune detections for unexpected outbound SSRF from Java application hosts followed by remote class loading activity; the SSRF→defineClass pattern is a distinct behavioral signal to hunt for in proxy and EDR telemetry.
Leader — Skip

Fastjson on CuraSec