Rule Definition
Insecure deserialization often leads to remote code execution. Even if deserialization flaws do not result in remote code execution, they can be used to perform attacks, including replay attacks, injection attacks, and privilege escalation attacks. The business impact depends on the protection needs of the application and data.

Remediation
Avoid serialising and deserialising objects Use signatures to detect tampering Configure your library safely As a last resort, restrict deserialization to be possible only to specific, whitelisted classes. Check out the OWASP Deserialisation Cheat Sheet

Violation Code Sample

Using readObject
________________

InputStream is; // value given by an API request
ObjectOutputStream ois = new ObjectOutputStream(is);
MyClass myclass1 = (MyClass)ois.readObject(); //Violation



Using XMLdecoder
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String userInput; // value given by an API request
XMLdecoder d = new XMLdecoder(
                            new BufferedInputStream(
                            new FileInputStream(userInput)));

Object result = d.readObject(); //Violation
d.close();


Using Kryo
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String userInput; // value given by an API request
Kryo kryo = new Kryo();
Output output = new Output(new FileOutputStream("file.dat"));
Input input = new input(new FileInputStream(userInput));
Object someObject = "some string";
kryo.writeClassAndObject(output, someObject);
output.close();
Object theObject = kryo.readClassAndObject(input);  //Violation
input.close();

Fixed Code Sample

Using readObject
________________

InputStream is; // is must not depend on API request
ObjectOutputStream ois = new ObjectOutputStream(is);
MyClass myclass1 = (MyClass)ois.readObject();



Using XMLdecoder
________________

XMLdecoder d = new XMLdecoder(
                            new BufferedInputStream(
                            new FileInputStream(file)));

Object result = d.readObject();
d.close();


Using Kryo
________________

String userInput = param;
Kryo kryo = new Kryo();
Output output = new Output(new FileOutputStream("file.dat"));
Input input = new input(new FileInputStream(file));
Object someObject = "some string";
kryo.writeClassAndObject(output, someObject);
output.close();
Object theObject = kryo.readClassAndObject(input);
input.close();

CWE-502: Deserialization of Untrusted Data https://cwe.mitre.org/data/definitions/502.html Open Web Application Security Project (OWASP) Top Ten 2017 - Category A8 https://owasp.org/www-project-top-ten/2017/A8_2017-Insecure_Deserialization