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.
Alternate Terms
Marshaling, Unmarshaling:
Marshaling and unmarshaling are effectively synonyms for serialization
and deserialization, respectively.
Pickling, Unpickling:
In Python, the "pickle" functionality is used to perform serialization
and deserialization.
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
Java
Ruby
PHP
Python
Language-independent
Common Consequences
Scope
Effect
Technical Impact: Varies by context
The consequences can vary widely, because it depends on which objects
or methods are being deserialized, and how they are used.
Integrity
Technical Impact: Modify application
data; Unexpected state
Attackers can modify unexpected objects or data that was assumed to be
safe from modification.
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 that make this dangerous
assumption could be exploited.
Likelihood of Exploit
Medium
Demonstrative Examples
Example 1
This code snippet deserializes an object from a file and uses it as
a UI button:
(Bad Code)
Example
Language: Java
try {
File file = new File("object.obj");
ObjectInputStream in = new ObjectInputStream(new
FileInputStream(file));
This code does not attempt to verify the source or contents of the
file before deserializing it. An attacker may be able to replace the
intended file with a file that contains arbitrary malicious code which
will be executed when the button is pressed.
Web browser allows execution of native methods via
a crafted string to a JavaScript function that deserializes the
string.
Potential Mitigations
Phases: Architecture and Design; Implementation
If available, use the signing/sealing features of the programming
language to assure that deserialized data has not been tainted. For
example, a hash-based message authentication code (HMAC) could be used
to ensure that data has not been modified.
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.
Background Details
Serialization and deserialization refer to the process of taking
program-internal object-related data, packaging it in a way that allows the
data to be externally stored or transferred ("serialization"), then
extracting the serialized data to reconstruct the original object
("deserialization").
The relationships between CWE-502 and CWE-915 need further exploration. CWE-915 is more narrowly scoped to object modification, and is not necessarily used for deserialization.
Description
