Attack Chain

1. Attacker crafts a malicious serialized Java object using a tool like ysoserial. For example, java -jar ysoserial.jar CommonsCollections6 "touch /tmp/pwned" > malicious_channel.ser.
2. The attacker gains the ability to supply crafted serialized Channel bytes to the client application. This could involve compromising a local channel file.
3. The attacker injects the malicious serialized data through an application that accepts Channel bytes from external sources.
4. The vulnerable deSerializeChannel() method in Channel.java is called with the attacker-controlled byte array.
5. Inside deSerializeChannel(), an ObjectInputStream is created from the byte array.
6. The readObject() method of ObjectInputStream is called without any ObjectInputFilter, deserializing the malicious object.
7. The deserialization process triggers the execution of a gadget chain embedded in the malicious object.
8. The gadget chain executes arbitrary code on the server, achieving RCE.

Impact

Successful exploitation of this vulnerability allows an attacker to execute arbitrary code on the server running the vulnerable fabric-sdk-java application. This can lead to complete system compromise, data breaches, and other malicious activities. The severity is critical due to the potential for unauthenticated remote code execution. Organizations still using the deprecated fabric-sdk-java are at high risk until they migrate to the supported fabric-gateway.

Recommendation

• Migrate to org.hyperledger.fabric:fabric-gateway immediately as the primary remediation, as it does not use Java serialization.
• For organizations unable to migrate immediately, apply the suggested fix of adding an ObjectInputFilter to whitelist only expected classes as described in the advisory.
• Implement runtime monitoring of Java deserialization to detect and prevent exploitation attempts.
• Enable logging of deserialization events to aid in incident response.