Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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CWE-404: Improper Resource Shutdown or Release

Weakness ID: 404
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The program does not release or incorrectly releases a resource before it is made available for re-use.
+ Extended Description
When a resource is created or allocated, the developer is responsible for properly releasing the resource as well as accounting for all potential paths of expiration or invalidation, such as a set period of time or revocation.
+ Relationships

The table(s) below 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 "Development Concepts" (CWE-699)
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Architecture and Design
+ Applicable Platforms
The listings below show 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.


(Language-Independent classes): (Undetermined Prevalence)

+ Common Consequences

The table below 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.


Technical Impact: DoS: Resource Consumption (Other); Varies by Context

Most unreleased resource issues result in general software reliability problems, but if an attacker can intentionally trigger a resource leak, the attacker might be able to launch a denial of service attack by depleting the resource pool.

Technical Impact: Read Application Data

When a resource containing sensitive information is not correctly shutdown, it may expose the sensitive data in a subsequent allocation.
+ Likelihood Of Exploit
+ Demonstrative Examples

Example 1

The following method never closes the file handle it opens. The Finalize() method for StreamReader eventually calls Close(), but there is no guarantee as to how long it will take before the Finalize() method is invoked. In fact, there is no guarantee that Finalize() will ever be invoked. In a busy environment, this can result in the VM using up all of its available file handles.

Example Language: Java 
private void processFile(string fName) {
StreamWriter sw = new StreamWriter(fName);
string line;
while ((line = sr.ReadLine()) != null){



Example 2

This code attempts to open a connection to a database and catches any exceptions that may occur.

Example Language: Java 
try {
Connection con = DriverManager.getConnection(some_connection_string);

catch ( Exception e ) {
log( e );


If an exception occurs after establishing the database connection and before the same connection closes, the pool of database connections may become exhausted. If the number of available connections is exceeded, other users cannot access this resource, effectively denying access to the application.

Example 3

Under normal conditions the following C# code executes a database query, processes the results returned by the database, and closes the allocated SqlConnection object. But if an exception occurs while executing the SQL or processing the results, the SqlConnection object is not closed. If this happens often enough, the database will run out of available cursors and not be able to execute any more SQL queries.

Example Language: C# 
SqlConnection conn = new SqlConnection(connString);
SqlCommand cmd = new SqlCommand(queryString);
cmd.Connection = conn;
SqlDataReader rdr = cmd.ExecuteReader();

Example 4

The following C function does not close the file handle it opens if an error occurs. If the process is long-lived, the process can run out of file handles.

Example Language:
int decodeFile(char* fName) {
char buf[BUF_SZ];
FILE* f = fopen(fName, "r");
if (!f) {
printf("cannot open %s\n", fName);

else {
while (fgets(buf, BUF_SZ, f)) {
if (!checkChecksum(buf)) {

else {





Example 5

In this example, the program does not use matching functions such as malloc/free, new/delete, and new[]/delete[] to allocate/deallocate the resource.

Example Language: C++ 
class A {
void foo();

void A::foo(){
int *ptr;
ptr = (int*)malloc(sizeof(int));
delete ptr;


Example 6

In this example, the program calls the delete[] function on non-heap memory.

Example Language: C++ 
class A{
void foo(bool);

void A::foo(bool heap) {
int localArray[2] = {

int *p = localArray;
if (heap){
p = new int[2];

delete[] p;

+ Observed Examples
Does not shut down named pipe connections if malformed data is sent.
Sockets not properly closed when attacker repeatedly connects and disconnects from server.
Return values of file/socket operations not checked, allowing resultant consumption of file descriptors.
+ Potential Mitigations

Phase: Requirements

Strategy: Language Selection

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.

Phase: Implementation

It is good practice to be responsible for freeing all resources you allocate and to be consistent with how and where you free memory in a function. If you allocate memory that you intend to free upon completion of the function, you must be sure to free the memory at all exit points for that function including error conditions.

Phase: Implementation

Memory should be allocated/freed using matching functions such as malloc/free, new/delete, and new[]/delete[].

Phase: Implementation

When releasing a complex object or structure, ensure that you properly dispose of all of its member components, not just the object itself.
+ Weakness Ordinalities
+ Detection Methods

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.

Resource clean up errors might be detected with a stress-test by calling the software simultaneously from a large number of threads or processes, and look for evidence of any unexpected behavior. 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.
+ Memberships
This 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.
+ Notes


Overlaps memory leaks, asymmetric resource consumption, malformed input errors.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERImproper resource shutdown or release
7 Pernicious KingdomsUnreleased Resource
OWASP Top Ten 2004A9CWE More SpecificDenial of Service
CERT C Secure CodingFIO42-CCWE More AbstractClose files when they are no longer needed
CERT C Secure CodingMEM31-CCWE More AbstractFree dynamically allocated memory when no longer needed
CERT Java Secure CodingFIO04-JRelease resources when they are no longer needed
Software Fault PatternsSFP14Failure to release resource
+ References
[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 8: C++ Catastrophes." Page 143. McGraw-Hill. 2010.
+ Content History
Submission DateSubmitterOrganizationSource
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigital
updated Time_of_Introduction
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITRE
updated Description, Relationships, Other_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Relationships
2008-11-24CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2009-01-12CWE Content TeamMITRE
updated Common_Consequences, Likelihood_of_Exploit, Other_Notes, Potential_Mitigations, Relationship_Notes, Relationships, Weakness_Ordinalities
2009-03-10CWE Content TeamMITRE
updated Potential_Mitigations
2009-05-27CWE Content TeamMITRE
updated Description, Relationships
2009-07-27CWE Content TeamMITRE
updated Demonstrative_Examples, Related_Attack_Patterns
2009-10-29CWE Content TeamMITRE
updated Other_Notes
2010-02-16CWE Content TeamMITRE
updated Potential_Mitigations, Relationships
2010-06-21CWE Content TeamMITRE
updated Detection_Factors, Potential_Mitigations
2010-12-13CWE Content TeamMITRE
updated Demonstrative_Examples
2011-03-29CWE Content TeamMITRE
updated Weakness_Ordinalities
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2011-06-27CWE Content TeamMITRE
updated Common_Consequences
2011-09-13CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, References, Relationships, Taxonomy_Mappings
2014-02-18CWE Content TeamMITRE
updated Demonstrative_Examples
2014-06-23CWE Content TeamMITRE
updated Related_Attack_Patterns
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITRE
updated Relationships
2017-01-19CWE Content TeamMITRE
updated Relationships
2017-05-03CWE Content TeamMITRE
updated Related_Attack_Patterns
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Functional_Areas, Likelihood_of_Exploit, Relationships, Taxonomy_Mappings

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Page Last Updated: November 14, 2017