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

What CVEs are caused by CWE-502?

2,227 recorded CVEs are attributed to CWE-502, including CVE-2025-26399, CVE-2025-53690, CVE-2025-24813. 68 are listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

What are the consequences of CWE-502?

Exploiting CWE-502 can lead to: Modify Application Data, Unexpected State, DoS: Resource Consumption (CPU), Varies by Context.

Is CWE-502 actively exploited?

Yes. 68 CWE-502 vulnerabilities are in CISA's KEV catalog of actively exploited flaws, out of 2,227 recorded CVEs.

CWE-502: Deserialization of Untrusted Data (Pickling, Unpickling)

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.

Background

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").

Real-world CVEs

2,227 recorded CVEs are caused by CWE-502 (Deserialization of Untrusted Data), including 68 in CISA's KEV (Known Exploited Vulnerabilities) catalog. KEVs are shown first. 608 new CWE-502 CVEs have been recorded so far in 2026 (635 in 2025).

Showing 12 of 2,227 recorded CWE-502 CVEs. Track new ones as they are published and get AI-written analysis and fixes.

Monitor CWE-502 vulnerabilities

Common consequences

What can happen when CWE-502 is exploited.

Modify Application Data, Unexpected State

Affects: Integrity

Attackers can modify unexpected objects or data that was assumed to be safe from modification. Deserialized data or code could be modified without using the provided accessor functions, or unexpected functions could be invoked.

DoS: Resource Consumption (CPU)

Affects: Availability

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

Varies by Context

Affects: Other

The consequences can vary widely, because it depends on which objects or methods are being deserialized, and how they are used. Making an assumption that the code in the deserialized object is valid is dangerous and can enable exploitation. One example is attackers using gadget chains to perform unauthorized actions, such as generating a shell.

How it happens

When it is introduced

Typically introduced during these phases of the software lifecycle.

Architecture and Design

Implementation

Applies to

Languages

Java

Ruby

PHP

Python

JavaScript

Technologies

ICS/OT (Often)

AI/ML (Often)

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.

How to detect it

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Effectiveness: High

Code examples

Illustrative examples from MITRE showing how the weakness appears in code.

This code snippet deserializes an object from a file and uses it as a UI button:

Vulnerable example

java

try {

Safe example

java

private final void readObject(ObjectInputStream in) throws java.io.IOException {

In Python, the Pickle library handles the serialization and deserialization processes. In this example derived from [REF-467], the code receives and parses data, and afterwards tries to authenticate a user based on validating a token.

Vulnerable example

python

try {

Unfortunately, the code does not verify that the incoming data is legitimate. An attacker can construct a illegitimate, serialized object "AuthToken" that instantiates one of Python's subprocesses to execute arbitrary commands. For instance,the attacker could construct a pickle that leverages Python's subprocess module, which spawns new processes and includes a number of arguments for various uses. Since Pickle allows objects to define the process for how they should be unpickled, the attacker can direct the unpickle process to call Popen in the subprocess module and execute /bin/sh.

Illustrative examples

Real CVEs that MITRE cites as examples of this weakness.

CVE-2015-4852
CISA KEV
— Deserialization issue in commonly-used Java library allows remote execution.
CVE-2024-37052 — insecure deserialization in platform for managing AI/ML applications and models allows code execution via a crafted pickled object in a model file
CVE-2024-37288 — deserialization of untrusted YAML data in dashboard for data query and visualization of Elasticsearch data
CVE-2024-9314 — PHP object injection in WordPress plugin for AI-based SEO
CVE-2019-12799 — chain: bypass of untrusted deserialization issue (CWE-502) by using an assumed-trusted class (CWE-183)
CVE-2015-8103 — Deserialization issue in commonly-used Java library allows remote execution.
CVE-2013-1465 — Use of PHP unserialize function on untrusted input allows attacker to modify application configuration.
CVE-2012-3527 — Use of PHP unserialize function on untrusted input in content management system might allow code execution.
CVE-2012-0911 — Use of PHP unserialize function on untrusted input in content management system allows code execution using a crafted cookie value.
CVE-2012-0911 — Content management system written in PHP allows unserialize of arbitrary objects, possibly allowing code execution.
CVE-2011-2520 — Python script allows local users to execute code via pickled data.
CVE-2012-4406 — Unsafe deserialization using pickle in a Python script.
CVE-2003-0791 — Web browser allows execution of native methods via a crafted string to a JavaScript function that deserializes the string.

How this weakness relates to others in the CWE hierarchy.

Parent

CWE-913: Improper Control of Dynamically-Managed Code Resources

Peer

CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes

Terminology & mappings

Alternate terms

Marshaling/Marshalling, Unmarshaling/Unmarshalling: 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.
PHP Object Injection: Some PHP application researchers use this term when attacking unsafe use of the unserialize() function; but it is also used for CWE-915.

Mapped taxonomies

CLASP: Deserialization of untrusted data
The CERT Oracle Secure Coding Standard for Java (2011): Do not deviate from the proper signatures of serialization methods (SER01-J)
The CERT Oracle Secure Coding Standard for Java (2011): Do not serialize unencrypted, sensitive data (SER03-J)
The CERT Oracle Secure Coding Standard for Java (2011): Make defensive copies of private mutable components during deserialization (SER06-J)
The CERT Oracle Secure Coding Standard for Java (2011): Do not use the default serialized form for implementation defined invariants (SER08-J)
Software Fault Patterns: Tainted input to variable (SFP25)

Attack patterns

CAPEC attack patterns that exploit this weakness.

CAPEC-586: Object Injection

Frequently asked questions

Common questions about CWE-502.

What is CWE-502?: The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
What CVEs are caused by CWE-502?: 2,227 recorded CVEs are attributed to CWE-502, including CVE-2025-26399, CVE-2025-53690, CVE-2025-24813. 68 are listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.
How do you prevent CWE-502?: 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.
How is CWE-502 detected?: Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
What are the consequences of CWE-502?: Exploiting CWE-502 can lead to: Modify Application Data, Unexpected State, DoS: Resource Consumption (CPU), Varies by Context.
Is CWE-502 actively exploited?: Yes. 68 CWE-502 vulnerabilities are in CISA's KEV catalog of actively exploited flaws, out of 2,227 recorded CVEs.

References

Weakness data is sourced from the MITRE CWE catalog (v4.20). CVE associations are aggregated and kept current by RadicalNotion.AI.

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

References

Stay ahead of CWE-502