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Home > CWE List > CWE-476: NULL Pointer Dereference (4.18)
ID
CWE Glossary Definition

CWE-476: NULL Pointer Dereference

Weakness ID: 476
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 dereferences a pointer that it expects to be valid but is NULL. Diagram for CWE-476
Alternate Terms
NPD
Common abbreviation for Null Pointer Dereference
null deref
Common abbreviation for Null Pointer Dereference
NPE
Common abbreviation for Null Pointer Exception
nil pointer dereference
used for access of nil in Go programs
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

DoS: Crash, Exit, or Restart

Scope: Availability

NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.

Execute Unauthorized Code or Commands; Read Memory; Modify Memory

Scope: Integrity, Confidentiality

In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
Potential Mitigations
Phase(s) Mitigation

Implementation
For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished [REF-1484].

Requirements
Select a programming language that is not susceptible to these issues.

Implementation
Check the results of all functions that return a value and verify that the value is non-null before acting upon it.

Effectiveness: Moderate

Note: Checking the return value of the function will typically be sufficient, however beware of race conditions (CWE-362) in a concurrent environment. This solution does not handle the use of improperly initialized variables (CWE-665).

Architecture and Design
Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values.

Implementation
Explicitly initialize all variables and other data stores, either during declaration or just before the first usage.
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 Pillar Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things. 710 Improper Adherence to Coding Standards
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. 754 Improper Check for Unusual or Exceptional Conditions
CanFollow 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. 252 Unchecked Return Value
CanFollow 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. 362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CanFollow Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. 789 Memory Allocation with Excessive Size Value
CanFollow 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. 1325 Improperly Controlled Sequential Memory Allocation
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. 465 Pointer Issues
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. 754 Improper Check for Unusual or Exceptional Conditions
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
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

C (Undetermined Prevalence)

C++ (Undetermined Prevalence)

Java (Undetermined Prevalence)

C# (Undetermined Prevalence)

Go (Undetermined Prevalence)

Likelihood Of Exploit
Medium
Demonstrative Examples

Example 1


This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

(bad code)
Example Language: C
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr;
char hostname[64];
in_addr_t inet_addr(const char *cp);

/*routine that ensures user_supplied_addr is in the right format for conversion */

validate_addr_form(user_supplied_addr);
addr = inet_addr(user_supplied_addr);
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET);
strcpy(hostname, hp->h_name);
}

If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy().

Note that this code is also vulnerable to a buffer overflow (CWE-119).



Example 2


In the following code, the programmer assumes that the system always has a property named "cmd" defined. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method.

(bad code)
Example Language: Java
String cmd = System.getProperty("cmd");
cmd = cmd.trim();


Example 3


This Android application has registered to handle a URL when sent an intent:

(bad code)
Example Language: Java

...
IntentFilter filter = new IntentFilter("com.example.URLHandler.openURL");
MyReceiver receiver = new MyReceiver();
registerReceiver(receiver, filter);
...

public class UrlHandlerReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
if("com.example.URLHandler.openURL".equals(intent.getAction())) {
String URL = intent.getStringExtra("URLToOpen");
int length = URL.length();

...
}
}
}

The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.



Example 4


Consider the following example of a typical client server exchange. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns.

(bad code)
Example Language: Go
func HandleRequest(client http.Client, request *http.Request) (*http.Response, error) {
response, err := client.Do(request)
defer response.Body.Close()
if err != nil {
return nil, err
}
...
}

If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err.

This HandleRequest Function evaluates the close before checking the error. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response.



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
race condition causes a table to be corrupted if a timer activates while it is being modified, leading to resultant NULL dereference; also involves locking.
large number of packets leads to NULL dereference
packet with invalid error status value triggers NULL dereference
Chain: race condition for an argument value, possibly resulting in NULL dereference
ssh component for Go allows clients to cause a denial of service (nil pointer dereference) against SSH servers.
Chain: Use of an unimplemented network socket operation pointing to an uninitialized handler function (CWE-456) causes a crash because of a null pointer dereference (CWE-476).
Chain: race condition (CWE-362) might allow resource to be released before operating on it, leading to NULL dereference (CWE-476)
Chain: some unprivileged ioctls do not verify that a structure has been initialized before invocation, leading to NULL dereference
Chain: IP and UDP layers each track the same value with different mechanisms that can get out of sync, possibly resulting in a NULL dereference
Chain: uninitialized function pointers can be dereferenced allowing code execution
Chain: improper initialization of memory can lead to NULL dereference
Chain: game server can access player data structures before initialization has happened leading to NULL dereference
Chain: The return value of a function returning a pointer is not checked for success (CWE-252) resulting in the later use of an uninitialized variable (CWE-456) and a null pointer dereference (CWE-476)
Chain: a message having an unknown message type may cause a reference to uninitialized memory resulting in a null pointer dereference (CWE-476) or dangling pointer (CWE-825), possibly crashing the system or causing heap corruption.
Chain: unchecked return value can lead to NULL dereference
SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference.
Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference.
Network monitor allows remote attackers to cause a denial of service (crash) via a malformed Q.931, which triggers a null dereference.
Chat client allows remote attackers to cause a denial of service (crash) via a passive DCC request with an invalid ID number, which causes a null dereference.
Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference.
OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection.
Game allows remote attackers to cause a denial of service (server crash) via a missing argument, which triggers a null pointer dereference.
Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference.
Chain: System call returns wrong value (CWE-393), leading to a resultant NULL dereference (CWE-476).
Weakness Ordinalities
Ordinality Description
Resultant
(where the weakness is typically related to the presence of some other weaknesses)
NULL pointer dereferences are frequently resultant from rarely encountered error conditions and race conditions, since these are most likely to escape detection during the testing phases.
Detection Methods
Method Details

Automated Dynamic Analysis
This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Effectiveness: Moderate

Manual Dynamic Analysis
Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Monitor the software for any unexpected behavior. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself.

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. 398 7PK - Code Quality
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 730 OWASP Top Ten 2004 Category A9 - Denial of Service
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 737 CERT C Secure Coding Standard (2008) Chapter 4 - Expressions (EXP)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 742 CERT C Secure Coding Standard (2008) Chapter 9 - Memory Management (MEM)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 808 2010 Top 25 - Weaknesses On the Cusp
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 867 2011 Top 25 - Weaknesses On the Cusp
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 871 CERT C++ Secure Coding Section 03 - Expressions (EXP)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 876 CERT C++ Secure Coding Section 08 - Memory Management (MEM)
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. 971 SFP Secondary Cluster: Faulty Pointer Use
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1136 SEI CERT Oracle Secure Coding Standard for Java - Guidelines 02. Expressions (EXP)
MemberOf CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic. 1157 SEI CERT C Coding Standard - Guidelines 03. Expressions (EXP)
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. 1306 CISQ Quality Measures - Reliability
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). 1350 Weaknesses in the 2020 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). 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. 1412 Comprehensive Categorization: Poor Coding Practices
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
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.
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
7 Pernicious Kingdoms Null Dereference
CLASP Null-pointer dereference
PLOVER Null Dereference (Null Pointer Dereference)
OWASP Top Ten 2004 A9 CWE More Specific Denial of Service
CERT C Secure Coding EXP34-C Exact Do not dereference null pointers
Software Fault Patterns SFP7 Faulty Pointer Use
References
[REF-6] Katrina Tsipenyuk, Brian Chess and Gary McGraw. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". NIST Workshop on Software Security Assurance Tools Techniques and Metrics. NIST. 2005年11月07日.
<https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf>.
[REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005.
<https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024年11月17日)
[REF-1031] "Null pointer / Null dereferencing". Wikipedia. 2019年07月15日.
<https://en.wikipedia.org/wiki/Null_pointer#Null_dereferencing>.
[REF-1032] "Null Reference Creation and Null Pointer Dereference". Apple.
<https://developer.apple.com/documentation/xcode/null-reference-creation-and-null-pointer-dereference>. (URL validated: 2023年04月07日)
[REF-1033] "NULL Pointer Dereference [CWE-476]". ImmuniWeb. 2012年09月11日.
<https://www.immuniweb.com/vulnerability/null-pointer-dereference.html>.
[REF-1484] D3FEND. "D3FEND: D3-NPC Null Pointer Checking".
<https://d3fend.mitre.org/technique/d3f:NullPointerChecking//>. (URL validated: 2025年09月08日)
Content History
Submissions
Submission Date Submitter Organization
2006年07月19日
(CWE Draft 3, 2006年07月19日) 		7 Pernicious Kingdoms
Contributions
Contribution Date Contributor Organization
2024年02月29日
(CWE 4.15, 2024年07月16日) 		Abhi Balakrishnan
Provided diagram to improve CWE usability
Modifications
Modification Date Modifier Organization
2025年09月09日
(CWE 4.18, 2025年09月09日) 		CWE Content Team MITRE
updated Potential_Mitigations, References
2025年04月03日
(CWE 4.17, 2025年04月03日) 		CWE Content Team MITRE
updated Demonstrative_Examples, Potential_Mitigations
2024年11月19日
(CWE 4.16, 2024年11月19日) 		CWE Content Team MITRE
updated Relationships
2024年07月16日
(CWE 4.15, 2024年07月16日) 		CWE Content Team MITRE
updated Alternate_Terms, Demonstrative_Examples, Description, Diagram, Potential_Mitigations, Relationships, Weakness_Ordinalities
2023年10月26日 CWE Content Team MITRE
updated Observed_Examples
2023年06月29日 CWE Content Team MITRE
updated Mapping_Notes, Relationships
2023年04月27日 CWE Content Team MITRE
updated Demonstrative_Examples, Detection_Factors, References, Relationships
2022年10月13日 CWE Content Team MITRE
updated Alternate_Terms, Applicable_Platforms, Observed_Examples
2022年06月28日 CWE Content Team MITRE
updated Relationships
2022年04月28日 CWE Content Team MITRE
updated Alternate_Terms
2021年07月20日 CWE Content Team MITRE
updated Relationships
2021年03月15日 CWE Content Team MITRE
updated Demonstrative_Examples, Observed_Examples
2020年12月10日 CWE Content Team MITRE
updated Relationships
2020年08月20日 CWE Content Team MITRE
updated Relationships
2020年06月25日 CWE Content Team MITRE
updated Common_Consequences
2020年02月24日 CWE Content Team MITRE
updated References
2019年09月19日 CWE Content Team MITRE
updated References, Relationships
2019年06月20日 CWE Content Team MITRE
updated Relationships
2019年01月03日 CWE Content Team MITRE
updated Relationships
2017年11月08日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings, White_Box_Definitions
2017年01月19日 CWE Content Team MITRE
updated Relationships
2015年12月07日 CWE Content Team MITRE
updated Relationships
2014年07月30日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2014年02月18日 CWE Content Team MITRE
updated Demonstrative_Examples
2012年05月11日 CWE Content Team MITRE
updated Observed_Examples, Related_Attack_Patterns, Relationships
2011年09月13日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2011年06月27日 CWE Content Team MITRE
updated Related_Attack_Patterns, Relationships
2011年06月01日 CWE Content Team MITRE
updated Common_Consequences
2010年12月13日 CWE Content Team MITRE
updated Relationships
2010年09月27日 CWE Content Team MITRE
updated Demonstrative_Examples, Observed_Examples, Relationships
2010年06月21日 CWE Content Team MITRE
updated Demonstrative_Examples, Description, Detection_Factors, Potential_Mitigations
2010年02月16日 CWE Content Team MITRE
updated Potential_Mitigations, Relationships
2009年12月28日 CWE Content Team MITRE
updated Common_Consequences, Demonstrative_Examples, Other_Notes, Potential_Mitigations, Weakness_Ordinalities
2009年10月29日 CWE Content Team MITRE
updated Relationships
2009年05月27日 CWE Content Team MITRE
updated Demonstrative_Examples
2008年11月24日 CWE Content Team MITRE
updated Relationships, Taxonomy_Mappings
2008年09月08日 CWE Content Team MITRE
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008年08月01日 KDM Analytics
added/updated white box definitions
2008年07月01日 Eric Dalci Cigital
updated Time_of_Introduction
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Page Last Updated: September 09, 2025

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