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Serialization and deserialization are standard practices, and they’re used in web applications regularly. Many programming languages even have native tools for serialization.
To create the best strategies for protecting your applications from insecure deserialization, it’s essential first to introduce and understand these two concepts.
Serialization means converting an object into a format for saving it to a file or database or sending it via streams or networks. This essential function regularly needs to be performed to store and transfer data. Programming languages serialize objects in different ways — using either binary or string formats.
The data has to be shaped in a certain way — preprocessed to a byte stream — which serialization does. Some standard serialization formats include XML and JSON.
The deserialization processes are just the opposite of serialization. They entail converting the serialized data from files, streams, or networks into an object. Deserialization essentially reconstructs the byte stream in the same state it was before being serialized.
This conversion is a typical process when done securely. Unsure deserialization should be avoided, in which malicious code comes from unauthorized user input.
This often happens when an attacker employs the customizable deserialization processes many programming languages offer to control them with untrusted input. Unfortunately, the languages presume the data is safe and treat all serialized data structures as validated, thus allowing the inclusion of malicious objects.
To protect your web application from insecure deserialization, it’s crucial never to pass a serialized object manipulated with untrusted input by the user to the deserialize function. The reason is that if you do so, an untrusted user would be able to manipulate the object and can send it directly to the PHP deserialize function.