Insecure Deserialization

Description

Vulnerable Code Example

Code:

String serializedData = request.getParameter("data");
ByteArrayInputStream bis = new ByteArrayInputStream(Base64.getDecoder().decode(serializedData));
ObjectInputStream ois = new ObjectInputStream(bis);
Object obj = ois.readObject();

• Line 1: String serializedData = request.getParameter("data");: Retrieves serialized data from the HTTP request parameter named “data”.
• Line 2: ByteArrayInputStream bis = new ByteArrayInputStream(Base64.getDecoder().decode(serializedData));: Decodes the serialized data from Base64 encoding and creates a ByteArrayInputStream.
• Line 3: ObjectInputStream ois = new ObjectInputStream(bis);: Constructs an ObjectInputStream to deserialize the data.
• Line 4: Object obj = ois.readObject();: Reads the deserialized object from the ObjectInputStream.

Mitigation Techniques

1. Implement Integrity Checks: Apply digital signatures or checksums to serialized objects to verify their integrity during deserialization.
2. Use Safe Deserialization Practices: Avoid deserializing untrusted data from unreliable sources and employ safe deserialization libraries or mechanisms.
3. Implement Whitelisting: Maintain a whitelist of permitted classes for deserialization and reject any serialized objects not belonging to the whitelist.

Note: Ensure deserialization is performed in a restricted environment with limited privileges. Validate deserialized data before processing it further to mitigate the risk of exploitation.

Code with Mitigation Implemented

Code:

String serializedData = request.getParameter("data");

// Decode the serialized data from Base64 encoding
byte[] serializedBytes = Base64.getDecoder().decode(serializedData);

try {
    // Use a safe deserialization mechanism, such as JSON deserialization, instead of ObjectInputStream
    Object obj = deserializeFromJSON(serializedBytes);
    
    // Use the deserialized object safely
} catch (IOException | ClassNotFoundException | ClassCastException ex) {
    // Handle deserialization errors
    // Respond with an error message or perform appropriate action
}

// Safe JSON deserialization method
private Object deserializeFromJSON(byte[] serializedBytes) throws IOException, ClassNotFoundException {
    // Deserialize the data from JSON format
    ObjectMapper objectMapper = new ObjectMapper();
    return objectMapper.readValue(serializedBytes, Object.class);
}

• Decode Serialized Data: Decode the serialized data from Base64 encoding to obtain the byte array representation.

• Use Safe Deserialization Mechanism: Instead of using ObjectInputStream for deserialization, employ a safer deserialization mechanism such as JSON deserialization. JSON deserialization libraries like Jackson or Gson provide better security controls and mitigate the risk of executing arbitrary code.

• Error Handling: Handle deserialization errors gracefully by catching exceptions (IOException, ClassNotFoundException, ClassCastException) and responding with appropriate error messages or actions.

References

• Waratek - What is a Java Deserialization Vulnerability?
• Red Fox Security - Insecure Deserialization in Java