The application deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
Extended Description
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security -- which is a dangerous security assumption.
Data that is untrusted can not be trusted to be well-formed.
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Availability
Technical Impact: DoS: resource consumption
(CPU)
If a function is making an assumption on when to terminate, based on a
sentry in a string, it could easily never terminate.
Authorization
Other
Technical Impact: Other
Code could potentially make the assumption that information in the
deserialized object is valid. Functions which make this dangerous
assumption could be exploited.
Likelihood of Exploit
Medium
Demonstrative Examples
Example 1
(Bad Code)
Example
Language: Java
try {
File file = new File("object.obj");
ObjectInputStream in = new ObjectInputStream(new
FileInputStream(file));
in = new ObjectInputStream(new
ByteArrayInputStream(bytes));
button = (javax.swing.JButton) in.readObject();
in.close();
}
Potential Mitigations
Phase: Requirements
A deserialization library could be used which provides a cryptographic
framework to seal serialized data.
Phase: Implementation
Use the signing features of a language to assure that deserialized
data has not been tainted.
Phase: Implementation
When deserializing data populate a new object rather than just
deserializing, the result is that the data flows through safe input
validation and that the functions are safe.
Phase: Implementation
Explicitly define final readObject() to prevent deserialization. An
example of this is:
(Good Code)
Example
Language: Java
private final void readObject(ObjectInputStream in) throws
java.io.IOException {
throw new java.io.IOException("Cannot be deserialized"); }
Phases: Architecture and Design; Implementation
Make fields transient to protect them from deserialization.
An attempt to serialize and then deserialize a class containing
transient fields will result in NULLs where the transient data should
be. This is an excellent way to prevent time, environment-based, or
sensitive variables from being carried over and used improperly.
Description
