Fastjson 1.2.68 and Earlier Remote Code Execution Vulnerability Threat Alert

Fastjson 1.2.68 and Earlier Remote Code Execution Vulnerability Threat Alert

junho 8, 2020 | Adeline Zhang

Vulnerability Description

On May 28, Fastjson 1.2.68 and before were reported to contain a remote code execution vulnerability that bypasses the autoType switch to implement deserialization of classes that contain security risks. Attackers could exploit this vulnerability to execute arbitrary code on the target machine.

Fastjson is an open-source JSON library developed by Alibaba to parse JOSN strings. It can be used to serialize JavaBean into a JSON string and deserialize a JSON string to JavaBean. Fastjson works efficiently and therefore is widely used. Users should take preventive measures as soon as possible.

 Scope of Impact

Affected Versions

  • Fastjson <= 1.2.68
  • Vulnerability Detection
  • Version Check

Users can use the following command to check the current Fastjson version:

lsof | grep fastjson

Note: In Fastjson 1.2.68, safeMode is introduced to make the autoType function useless.


  • Workarounds

The vendor has not patched this vulnerability. Affected users can disable autoType and upgrade the JDK to the latest version for risk aversion.

As the autoType switch can be bypassed, affected users should upgrade Fastjson to 1.2.68 and activate safeMode to disable autoType. safeMode can be configured in one of the following ways:

  • Configure safeMode in the code:
  • Add the JVM startup parameter:

If there are multiple package name prefixes, separate them with commas (,).

  • Use the file in the class path for configuration:

Add risky classes to the blacklist for protection:

ParserConfig.getGlobalInstance().addDeny(“class name”);

Users of this software are advised to watch for Fastjson’s security advisory and load the update as soon as it is available to protect against this vulnerability. Download link:


This advisory is only used to describe a potential risk. NSFOCUS does not provide any commitment or promise on this advisory. NSFOCUS and the author will not bear any liability for any direct and/or indirect consequences and losses caused by transmitting and/or using this advisory. NSFOCUS reserves all the rights to modify and interpret this advisory. Please include this statement paragraph when reproducing or transferring this advisory. Do not modify this advisory, add/delete any information to/from it, or use this advisory for commercial purposes without permission from NSFOCUS.


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