Deserialization of Untrusted Data
Weakness ID: 502 (Weakness Variant)Status: Draft
+ Description

Description Summary

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



+ Common Consequences

If a function is making an assumption on when to terminate, based on a sentry in a string, it could easily never terminate.


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


+ Demonstrative Examples

Example 1

(Bad Code)
Example Language: Java 
try {
File file = new File("object.obj");
ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
javax.swing.JButton button = (javax.swing.JButton) in.readObject();
byte[] bytes = getBytesFromFile(file);
in = new ObjectInputStream(new ByteArrayInputStream(bytes));
button = (javax.swing.JButton) in.readObject();
+ 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 {
throw new"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.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class485Insufficient Encapsulation
Development Concepts (primary)699
Research Concepts (primary)1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPDeserialization of untrusted data
+ Content History
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Common Consequences, Description, Relationships, Other Notes, Taxonomy Mappings
2009-10-29CWE Content TeamMITREInternal
updated Description, Other Notes, Potential Mitigations