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Common Weakness Enumeration

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ID

CWE-502: Deserialization of Untrusted Data

Weakness ID: 502
Vulnerability Mapping: ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities
Abstraction: BaseBase - 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 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.

When developers place no restrictions on "gadget chains," or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.

+ 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.
+ Relationships
Section HelpThis 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" (CWE-1000)
NatureTypeIDName
ChildOfClassClass - 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.913Improper Control of Dynamically-Managed Code Resources
PeerOfBaseBase - 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.915Improperly Controlled Modification of Dynamically-Determined Object Attributes
Section HelpThis 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 "Software Development" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.399Resource Management Errors
Section HelpThis 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
NatureTypeIDName
ChildOfClassClass - 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.913Improper Control of Dynamically-Managed Code Resources
Section HelpThis 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 "Architectural Concepts" (CWE-1008)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1019Validate 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.
PhaseNote
Architecture and DesignOMISSION: 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: ICS/OT (Often Prevalent)

+ 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.
ScopeImpactLikelihood
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.
Other

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. Making an assumption that the code in the deserialized object is valid is dangerous and can enable exploitation.
+ 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.

+ Observed Examples
ReferenceDescription
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.
+ 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 a final object() to prevent deserialization.

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.

Phase: Implementation

Avoid having unnecessary types or gadgets 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.
+ Detection Methods

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.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.858The CERT Oracle Secure Coding Standard for Java (2011) Chapter 15 - Serialization (SER)
MemberOfViewView - 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).884CWE Cross-section
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.994SFP Secondary Cluster: Tainted Input to Variable
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1034OWASP Top Ten 2017 Category A8 - Insecure Deserialization
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1148SEI CERT Oracle Secure Coding Standard for Java - Guidelines 14. Serialization (SER)
MemberOfViewView - 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).1200Weaknesses in the 2019 CWE Top 25 Most Dangerous Software Errors
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1308CISQ Quality Measures - Security
MemberOfViewView - 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).1337Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses
MemberOfViewView - 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).1340CISQ Data Protection Measures
MemberOfViewView - 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).1350Weaknesses in the 2020 CWE Top 25 Most Dangerous Software Weaknesses
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1354OWASP Top Ten 2021 Category A08:2021 - Software and Data Integrity Failures
MemberOfViewView - 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).1387Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1415Comprehensive Categorization: Resource Control
MemberOfViewView - 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).1425Weaknesses in the 2023 CWE Top 25 Most Dangerous Software Weaknesses
+ Vulnerability Mapping Notes

Usage: ALLOWED

(this CWE ID could 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 NameNode IDFitMapped Node Name
CLASPDeserialization of untrusted data
The CERT Oracle Secure Coding Standard for Java (2011)SER01-JDo not deviate from the proper signatures of serialization methods
The CERT Oracle Secure Coding Standard for Java (2011)SER03-JDo not serialize unencrypted, sensitive data
The CERT Oracle Secure Coding Standard for Java (2011)SER06-JMake defensive copies of private mutable components during deserialization
The CERT Oracle Secure Coding Standard for Java (2011)SER08-JDo not use the default serialized form for implementation defined invariants
Software Fault PatternsSFP25Tainted input to variable
+ References
[REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005. <https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>.
[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.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2006-07-19
(CWE Draft 3, 2006-07-19)
CLASP
+ Modifications
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Common_Consequences, Description, Relationships, Other_Notes, Taxonomy_Mappings
2009-10-29CWE Content TeamMITRE
updated Description, Other_Notes, Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-10-30CWE Content TeamMITRE
updated Demonstrative_Examples
2013-02-21CWE Content TeamMITRE
updated Alternate_Terms, Applicable_Platforms, Background_Details, Common_Consequences, Maintenance_Notes, Observed_Examples, Potential_Mitigations, References, Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITRE
updated Observed_Examples, References, Relationships
2017-05-03CWE Content TeamMITRE
updated Applicable_Platforms, Demonstrative_Examples, Description, Potential_Mitigations, References
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Modes_of_Introduction, Potential_Mitigations, References, Relationships
2018-03-27CWE Content TeamMITRE
updated Relationships
2019-01-03CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships, Taxonomy_Mappings
2019-06-20CWE Content TeamMITRE
updated Type
2019-09-19CWE Content TeamMITRE
updated Relationships
2020-02-24CWE Content TeamMITRE
updated Observed_Examples, References, Relationships
2020-06-25CWE Content TeamMITRE
updated Alternate_Terms, Potential_Mitigations
2020-08-20CWE Content TeamMITRE
updated Relationships
2020-12-10CWE Content TeamMITRE
updated Relationships
2021-07-20CWE Content TeamMITRE
updated Relationships
2021-10-28CWE Content TeamMITRE
updated Relationships
2022-06-28CWE Content TeamMITRE
updated Relationships
2022-10-13CWE Content TeamMITRE
updated Applicable_Platforms
2023-01-31CWE Content TeamMITRE
updated Description
2023-04-27CWE Content TeamMITRE
updated Detection_Factors, References, Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes, Relationships
Page Last Updated: February 29, 2024