CWE - CWE-502: Deserialization of Untrusted Data (4.19.1)
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    CWE-502: Deserialization of Untrusted Data

    Weakness ID: 502
    Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
    Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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    + Description
    The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid. Diagram for CWE-502
    + 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.
    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.
    + Common Consequences
    Section HelpThis table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
    Impact Details

    Modify Application Data; Unexpected State

    		Scope: 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)

    		Scope: 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

    		Scope: 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.
    + Potential Mitigations
    Phase(s) Mitigation

    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

    Strategy: 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

    Note: 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.
    + Relationships
    Section Help This table shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.
    + Relevant to the view "Research Concepts" (View-1000)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 913 Improper Control of Dynamically-Managed Code Resources
    PeerOf Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. 915 Improperly Controlled Modification of Dynamically-Determined Object Attributes
    + Relevant to the view "Software Development" (View-699)
    Nature Type ID Name
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 399 Resource Management Errors
    + Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (View-1003)
    Nature Type ID Name
    ChildOf Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. 913 Improper Control of Dynamically-Managed Code Resources
    + Relevant to the view "Architectural Concepts" (View-1008)
    Nature Type ID Name
    MemberOf Category Category - a CWE entry that contains a set of other entries that share a common characteristic. 1019 Validate Inputs
    + 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").
    + Modes Of Introduction
    Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.
    Phase Note
    Architecture and Design OMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.
    Implementation
    + Applicable Platforms
    Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.
    Languages

    Java (Undetermined Prevalence)

    Ruby (Undetermined Prevalence)

    PHP (Undetermined Prevalence)

    Python (Undetermined Prevalence)

    JavaScript (Undetermined Prevalence)

    Technologies

    Class: Not Technology-Specific (Undetermined Prevalence)

    Class: ICS/OT (Often Prevalent)

    AI/ML (Often Prevalent)

    + 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));
    javax.swing.JButton button = (javax.swing.JButton) in.readObject();
    in.close();
    }

    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.

    To mitigate this, 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"); }


    Example 2


    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.

    (bad code)
    Example Language: Python 
    try {
    class ExampleProtocol(protocol.Protocol):
    def dataReceived(self, data):

    # Code that would be here would parse the incoming data
    # After receiving headers, call confirmAuth() to authenticate

    def confirmAuth(self, headers):
    try:
    token = cPickle.loads(base64.b64decode(headers['AuthToken']))
    if not check_hmac(token['signature'], token['data'], getSecretKey()):
    raise AuthFail
    self.secure_data = token['data']
    except:
    raise AuthFail
    }

    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.



    + Selected Observed Examples

    Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

    Reference Description
    insecure deserialization in platform for managing AI/ML applications and models allows code execution via a crafted pickled object in a model file
    deserialization of untrusted YAML data in dashboard for data query and visualization of Elasticsearch data
    PHP object injection in WordPress plugin for AI-based SEO
    chain: bypass of untrusted deserialization issue (CWE-502) by using an assumed-trusted class (CWE-183)
    Deserialization issue in commonly-used Java library allows remote execution.
    Deserialization issue in commonly-used Java library allows remote execution.
    Use of PHP unserialize function on untrusted input allows attacker to modify application configuration.
    Use of PHP unserialize function on untrusted input in content management system might allow code execution.
    Use of PHP unserialize function on untrusted input in content management system allows code execution using a crafted cookie value.
    Content management system written in PHP allows unserialize of arbitrary objects, possibly allowing code execution.
    Python script allows local users to execute code via pickled data.
    Unsafe deserialization using pickle in a Python script.
    Web browser allows execution of native methods via a crafted string to a JavaScript function that deserializes the string.
    + Weakness Ordinalities
    Ordinality Description
    Primary
    (where the weakness exists independent of other weaknesses)
    Resultant
    (where the weakness is typically related to the presence of some other weaknesses)
    + Detection Methods
    Method Details

    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
    + Memberships
    Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
    Nature Type ID Name
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 858 The CERT Oracle Secure Coding Standard for Java (2011) Chapter 15 - Serialization (SER)
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 884 CWE Cross-section
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 994 SFP Secondary Cluster: Tainted Input to Variable
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1034 OWASP Top Ten 2017 Category A8 - Insecure Deserialization
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1148 SEI CERT Oracle Secure Coding Standard for Java - Guidelines 14. Serialization (SER)
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1200 Weaknesses in the 2019 CWE Top 25 Most Dangerous Software Errors
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1308 CISQ Quality Measures - Security
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1337 Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1340 CISQ Data Protection Measures
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1350 Weaknesses in the 2020 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1354 OWASP Top Ten 2021 Category A08:2021 - Software and Data Integrity Failures
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1387 Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1415 Comprehensive Categorization: Resource Control
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1425 Weaknesses in the 2023 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1430 Weaknesses in the 2024 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf ViewView - a subset of CWE entries that provides a way of examining CWE content. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). 1435 Weaknesses in the 2025 CWE Top 25 Most Dangerous Software Weaknesses
    MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1443 OWASP Top Ten 2025 Category A08:2025 - Software or Data Integrity Failures
    + Vulnerability Mapping Notes
    Usage ALLOWED
    (this CWE ID may be used to map to real-world vulnerabilities)
    Reason Acceptable-Use

    Rationale

    		This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.

    Comments

    		Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.
    + Notes

    Maintenance

    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.
    + Taxonomy Mappings
    Mapped Taxonomy Name Node ID Fit Mapped Node Name
    CLASP Deserialization of untrusted data
    The CERT Oracle Secure Coding Standard for Java (2011) SER01-J Do not deviate from the proper signatures of serialization methods
    The CERT Oracle Secure Coding Standard for Java (2011) SER03-J Do not serialize unencrypted, sensitive data
    The CERT Oracle Secure Coding Standard for Java (2011) SER06-J Make defensive copies of private mutable components during deserialization
    The CERT Oracle Secure Coding Standard for Java (2011) SER08-J Do not use the default serialized form for implementation defined invariants
    Software Fault Patterns SFP25 Tainted input to variable
    + References
    [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005.
    <https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024-11-17)
    [REF-461] Matthias Kaiser. "Exploiting Deserialization Vulnerabilities in Java". 2015-10-28.
    <https://www.slideshare.net/codewhitesec/exploiting-deserialization-vulnerabilities-in-java-54707478>. (URL validated: 2023-04-07)
    [REF-462] Sam Thomas. "PHP unserialization vulnerabilities: What are we missing?". 2015-08-27.
    <https://www.slideshare.net/_s_n_t/php-unserialization-vulnerabilities-what-are-we-missing>. (URL validated: 2023-04-07)
    [REF-463] Gabriel Lawrence and Chris Frohoff. "Marshalling Pickles: How deserializing objects can ruin your day". 2015-01-28.
    <https://www.slideshare.net/frohoff1/appseccali-2015-marshalling-pickles>. (URL validated: 2023-04-07)
    [REF-464] Heine Deelstra. "Unserializing user-supplied data, a bad idea". 2010-08-25.
    <https://drupalsun.com/heine/2010/08/25/unserializing-user-supplied-data-bad-idea>. (URL validated: 2023-04-07)
    [REF-465] Manish S. Saindane. "Black Hat EU 2010 - Attacking Java Serialized Communication". 2010-04-26.
    <https://www.slideshare.net/msaindane/black-hat-eu-2010-attacking-java-serialized-communication>. (URL validated: 2023-04-07)
    [REF-466] Nadia Alramli. "Why Python Pickle is Insecure". 2009-09-09.
    <http://michael-rushanan.blogspot.com/2012/10/why-python-pickle-is-insecure.html>. (URL validated: 2023-04-07)
    [REF-467] Nelson Elhage. "Exploiting misuse of Python's "pickle"". 2011-03-20.
    <https://blog.nelhage.com/2011/03/exploiting-pickle/>.
    [REF-468] Chris Frohoff. "Deserialize My Shorts: Or How I Learned to Start Worrying and Hate Java Object Deserialization". 2016-03-21.
    <https://speakerdeck.com/frohoff/owasp-sd-deserialize-my-shorts-or-how-i-learned-to-start-worrying-and-hate-java-object-deserialization>. (URL validated: 2023-04-07)
    [REF-1481] D3FEND. "D3FEND: Application Layer Firewall".
    <https://d3fend.mitre.org/dao/artifact/d3f:ApplicationLayerFirewall/>. (URL validated: 2025-09-06)
    + Content History
    + Submissions
    Submission Date Submitter Organization
    2006-07-19
    (CWE Draft 3, 2006-07-19)     		CLASP
    + Contributions
    Contribution Date Contributor Organization
    2024-02-29
    (CWE 4.16, 2024-11-19)     		Abhi Balakrishnan
    Contributed usability diagram concepts used by the CWE team
    + Modifications
    Modification Date Modifier Organization
    2025-12-11
    (CWE 4.19, 2025-12-11)     		CWE Content Team MITRE
    updated Applicable_Platforms, Observed_Examples, Relationships, Weakness_Ordinalities
    2025-09-09
    (CWE 4.18, 2025-09-09)     		CWE Content Team MITRE
    updated Observed_Examples, Potential_Mitigations, References
    2024-11-19
    (CWE 4.16, 2024-11-19)     		CWE Content Team MITRE
    updated Common_Consequences, Description, Diagram, Potential_Mitigations, Relationships
    2023-06-29 CWE Content Team MITRE
    updated Mapping_Notes, Relationships
    2023-04-27 CWE Content Team MITRE
    updated Detection_Factors, References, Relationships
    2023-01-31 CWE Content Team MITRE
    updated Description
    2022-10-13 CWE Content Team MITRE
    updated Applicable_Platforms
    2022-06-28 CWE Content Team MITRE
    updated Relationships
    2021-10-28 CWE Content Team MITRE
    updated Relationships
    2021-07-20 CWE Content Team MITRE
    updated Relationships
    2020-12-10 CWE Content Team MITRE
    updated Relationships
    2020-08-20 CWE Content Team MITRE
    updated Relationships
    2020-06-25 CWE Content Team MITRE
    updated Alternate_Terms, Potential_Mitigations
    2020-02-24 CWE Content Team MITRE
    updated Observed_Examples, References, Relationships
    2019-09-19 CWE Content Team MITRE
    updated Relationships
    2019-06-20 CWE Content Team MITRE
    updated Type
    2019-01-03 CWE Content Team MITRE
    updated Related_Attack_Patterns, Relationships, Taxonomy_Mappings
    2018-03-27 CWE Content Team MITRE
    updated Relationships
    2017-11-08 CWE Content Team MITRE
    updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Modes_of_Introduction, Potential_Mitigations, References, Relationships
    2017-05-03 CWE Content Team MITRE
    updated Applicable_Platforms, Demonstrative_Examples, Description, Potential_Mitigations, References
    2015-12-07 CWE Content Team MITRE
    updated Observed_Examples, References, Relationships
    2014-07-30 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2013-02-21 CWE Content Team MITRE
    updated Alternate_Terms, Applicable_Platforms, Background_Details, Common_Consequences, Maintenance_Notes, Observed_Examples, Potential_Mitigations, References, Relationships
    2012-10-30 CWE Content Team MITRE
    updated Demonstrative_Examples
    2012-05-11 CWE Content Team MITRE
    updated Relationships, Taxonomy_Mappings
    2011-06-01 CWE Content Team MITRE
    updated Common_Consequences, Relationships, Taxonomy_Mappings
    2009-10-29 CWE Content Team MITRE
    updated Description, Other_Notes, Potential_Mitigations
    2008-09-08 CWE Content Team MITRE
    updated Common_Consequences, Description, Relationships, Other_Notes, Taxonomy_Mappings
    2008-07-01 Eric Dalci Cigital
    updated Time_of_Introduction
    Page Last Updated: January 21, 2026