Base weakness

Draft

CWE-502: Deserialization of Untrusted Data

Also known as: Marshaling/Marshalling, Unmarshaling/Unmarshalling, Pickling, Unpickling, PHP Object Injection

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

1,979

Recorded CVEs

With this primary weakness

KEVs

In the CISA KEV catalog

Medium

Likelihood of exploit

Per MITRE

Base

Abstraction

MITRE classification

Overview

CWE-502 (Deserialization of Untrusted Data) is a base-level software weakness catalogued by MITRE in the Common Weakness Enumeration (CWE). It describes a recurring type of mistake that can lead to exploitable security vulnerabilities.

How to prevent it

Practical mitigations for CWE-502, grouped by where in the lifecycle they apply.

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.

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.

Implementation

Explicitly define a final object() to prevent deserialization.

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.

Implementation

Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.

Architecture and Design

Implementation

Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.

Operation

Firewall

Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].

Effectiveness: Moderate — An application firewall might not cover all possible input vectors. In addition, attack techniques might be available to bypass the protection mechanism, such as using malformed inputs that can still be processed by the component that receives those inputs. Depending on functionality, an application firewall might inadvertently reject or modify legitimate requests. Finally, some manual effort may be required for customization.

CWE-502: Deserialization of Untrusted Data

Overview

Background

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Code examples

Illustrative examples

Terminology & mappings

Alternate terms

Mapped taxonomies

Attack patterns

Frequently asked questions

What is CWE-502?

What CVEs are caused by CWE-502?

How do you prevent CWE-502?

How is CWE-502 detected?

What are the consequences of CWE-502?

Is CWE-502 actively exploited?

References

Stay ahead of CWE-502

Overview

Background

Real-world CVEs

Common consequences

How it happens

When it is introduced

Applies to

How to prevent it

How to detect it

Automated Static Analysis

Code examples

Illustrative examples

Related weaknesses

Parent

Peer

Terminology & mappings

Alternate terms

Mapped taxonomies

Attack patterns

Frequently asked questions

What is CWE-502?

What CVEs are caused by CWE-502?

How do you prevent CWE-502?

How is CWE-502 detected?

What are the consequences of CWE-502?

Is CWE-502 actively exploited?

References

Stay ahead of CWE-502