CWE-404: Improper Resource Shutdown or Release
The product does not release or incorrectly releases a resource before it is made available for re-use.
View on MITREExtended 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.
Technical Details
- Structure
- Simple
Applicable To
Security Consequences
Scope
Impact
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.
Scope
Impact
When a resource containing sensitive information is not correctly shutdown, it may expose the sensitive data in a subsequent allocation.
Mitigation Strategies
Phase
Description
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
Description
Memory should be allocated/freed using matching functions such as malloc/free, new/delete, and new[]/delete[].
Phase
Description
When releasing a complex object or structure, ensure that you properly dispose of all of its member components, not just the object itself.
Detection Methods
No detection method information available for this CWE.
Code Examples & CVEs
Demonstrative Examples
The following method never closes the new file handle. Given enough time, the Finalize() method for BufferReader should eventually call Close(), but there is no guarantee as to how long this action will take. In fact, there is no guarantee that Finalize() will ever be invoked. In a busy environment, the Operating System could use up all of the available file handles before the Close() function is called.
The good code example simply adds an explicit call to the Close() function when the system is done using the file. Within a simple example such as this the problem is easy to see and fix. In a real system, the problem may be considerably more obscure.
The following method never closes the new file handle. Given enough time, the Finalize() method for BufferReader should eventually call Close(), but there is no guarantee as to how long this action will take. In fact, there is no guarantee that Finalize() will ever be invoked. In a busy environment, the Operating System could use up all of the available file handles before the Close() function is called.
The good code example simply adds an explicit call to the Close() function when the system is done using the file. Within a simple example such as this the problem is easy to see and fix. In a real system, the problem may be considerably more obscure.
This code attempts to open a connection to a database and catches any exceptions that may occur.
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.
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.
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.
In this example, the program does not use matching functions such as malloc/free, new/delete, and new[]/delete[] to allocate/deallocate the resource.
In this example, the program calls the delete[] function on non-heap memory.
Observed CVE Examples (3)
Sockets not properly closed when attacker repeatedly connects and disconnects from server.
View DetailsChain: Return values of file/socket operations are not checked (CWE-252), allowing resultant consumption of file descriptors (CWE-772).
View DetailsCWE Relationships
No relationship information available for this CWE.
Frequently Asked Questions
What is CWE-404: Improper Resource Shutdown or Release?+
CWE-404: Improper Resource Shutdown or Release is a Common Weakness Enumeration (CWE) entry maintained by MITRE. The product does not release or incorrectly releases a resource before it is made available for re-use. 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.
What are the security consequences of Improper Resource Shutdown or Release?+
If exploited, CWE-404 (Improper Resource Shutdown or Release) it can compromise Availability, Other and Confidentiality, leading to outcomes such as DoS: Resource Consumption (Other), Varies by Context and Read Application Data.
How do you prevent or mitigate Improper Resource Shutdown or Release?+
Recommended mitigations for CWE-404 include: 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. Memory should be allocated/freed using matching functions such as malloc/free, new/delete, and new[]/delete[]. When releasing a complex object or structure, ensure that you properly dispose of all of its member components, not just the object itself.
Which programming languages are affected by Improper Resource Shutdown or Release?+
CWE-404 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
What are real-world examples of Improper Resource Shutdown or Release?+
MITRE documents real CVEs mapped to CWE-404, including CVE-1999-1127, CVE-2001-0830 and CVE-2002-1372. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
What is the difference between a CWE and a CVE?+
A CWE (Common Weakness Enumeration) like CWE-404 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.