Summary

This advisory covers the deprecated fabric-sdk-java client SDK. Channel.java implements readObject() and exposes deSerializeChannel() which call ObjectInputStream.readObject() on untrusted byte arrays without configuring an ObjectInputFilter. This is the classic Java deserialization RCE pattern.

Note: fabric-sdk-java is deprecated and maintained in https://github.com/hyperledger/fabric-sdk-java. Filing here as that repo does not have private vulnerability reporting enabled.

Affected Code

// src/main/java/org/hyperledger/fabric/sdk/Channel.java
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
    in.defaultReadObject();  // No ObjectInputFilter configured
}

public Channel deSerializeChannel(byte[] channelBytes)
        throws IOException, ClassNotFoundException, InvalidArgumentException {
    ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(channelBytes));
    Channel channel = (Channel) ois.readObject();  // Untrusted bytes deserialized
    return channel;
}

Attack Vector

An attacker who can supply crafted serialized Channel bytes to the client application — for example, by compromising a local channel file, injecting data through an application that accepts Channel bytes from external sources, or exploiting a separate write primitive — can achieve RCE via gadget chain exploitation when deSerializeChannel() processes those bytes. The risk is highest in deployments that accept Channel data from sources outside the client's direct control. Note: channel data is not transmitted from Fabric peers; this is a client-side deserialization surface.

Proof of Concept

// Generate malicious payload with ysoserial:
// java -jar ysoserial.jar CommonsCollections6 "touch /tmp/pwned" > malicious_channel.ser

// Victim code:
byte[] maliciousBytes = Files.readAllBytes(Paths.get("malicious_channel.ser"));
Channel channel = client.deSerializeChannel(maliciousBytes);  // RCE fires here

Notes on Deprecation

fabric-sdk-java is deprecated as of Hyperledger Fabric v2.5 (replaced by org.hyperledger.fabric:fabric-gateway). However, organizations that have not yet migrated remain fully exposed. Automated dependency scanners (Snyk, Dependabot) cannot alert users without a published GHSA. This advisory is filed to ensure those users are notified and directed to migrate.

Fix

For the deprecated SDK: add ObjectInputFilter to whitelist only expected classes:

ObjectInputFilter filter = ObjectInputFilter.Config.createFilter(
    "org.hyperledger.fabric.sdk.*;java.util.*;java.lang.*;!*"
);
ois.setObjectInputFilter(filter);

The recommended remediation is migration to org.hyperledger.fabric:fabric-gateway, which does not use Java serialization.

References

• CWE-502: Deserialization of Untrusted Data
• Migration guide: https://hyperledger.github.io/fabric-gateway/

Credits

Found via independent security research.