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.
CWE-404 Class Draft
Improper Resource Shutdown or Release
This vulnerability occurs when a program fails to properly close or release a system resource—like a file handle, database connection, or memory block—after it's no longer needed, preventing its…
Definition
What is CWE-404?
This vulnerability occurs when a program fails to properly close or release a system resource—like a file handle, database connection, or memory block—after it's no longer needed, preventing its reuse.
Developers must actively manage a resource's entire lifecycle, from allocation to release. This means ensuring cleanup happens not just in the main success path, but also in every possible error or exception scenario. Missing a single code path can leave resources permanently locked, leading to gradual performance degradation or sudden application crashes.
Tracking these leaks across complex, distributed systems is challenging. While SAST tools can flag the pattern, Plexicus uses AI to analyze context and suggest precise code fixes—such as adding finally blocks or implementing try-with-resources—automating remediation and saving hours of manual debugging.
Real-world impact
Real-world CVEs caused by CWE-404
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Does not shut down named pipe connections if malformed data is sent.
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Sockets not properly closed when attacker repeatedly connects and disconnects from server.
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Chain: Return values of file/socket operations are not checked (CWE-252), allowing resultant consumption of file descriptors (CWE-772).
How attackers exploit it
Step-by-step attacker path
- 1
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.
- 2
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.
- 3
This code attempts to open a connection to a database and catches any exceptions that may occur.
- 4
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.
- 5
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.
Vulnerable code example
Vulnerable Java
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.
private void processFile(string fName)
{
BufferReader fil = new BufferReader(new FileReader(fName));
String line;
while ((line = fil.ReadLine()) != null)
{
processLine(line);
}
} Secure code example
Secure Java
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.
private void processFile(string fName)
{
BufferReader fil = new BufferReader(new FileReader(fName));
String line;
while ((line = fil.ReadLine()) != null)
{
processLine(line);
}
fil.Close();
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-404
- Requirements 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.
- 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.
- Implementation Memory should be allocated/freed using matching functions such as malloc/free, new/delete, and new[]/delete[].
- Implementation When releasing a complex object or structure, ensure that you properly dispose of all of its member components, not just the object itself.
Detection signals
How to detect CWE-404
Identify error conditions that are not likely to occur during normal usage and trigger them. For example, run the product 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, 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.)
Plexicus auto-detects CWE-404 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-404?
How serious is CWE-404?
What languages or platforms are affected by CWE-404?
How can I prevent CWE-404?
How does Plexicus detect and fix CWE-404?
Where can I learn more about CWE-404?
Frequently asked questions
What is CWE-404?
This vulnerability occurs when a program fails to properly close or release a system resource—like a file handle, database connection, or memory block—after it's no longer needed, preventing its reuse.
How serious is CWE-404?
MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.
What languages or platforms are affected by CWE-404?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-404?
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. 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…
How does Plexicus detect and fix CWE-404?
Plexicus's SAST engine matches the data-flow signature for CWE-404 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-404?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/404.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-404
CWE-664 Parent
Improper Control of a Resource Through its Lifetime
This vulnerability occurs when software fails to properly manage a resource throughout its entire lifecycle—from creation and active use…
CWE-118 Sibling
Incorrect Access of Indexable Resource ('Range Error')
This vulnerability occurs when software fails to properly check the boundaries of an indexed resource, like an array, buffer, or file,…
CWE-1229 Sibling
Creation of Emergent Resource
This vulnerability occurs when a system's normal operations unintentionally create new, exploitable resources that attackers can use to…
CWE-1250 Sibling
Improper Preservation of Consistency Between Independent Representations of Shared State
This vulnerability occurs when a system with multiple independent components (like distributed services or separate hardware units) each…
CWE-1329 Sibling
Reliance on Component That is Not Updateable
This vulnerability occurs when a product depends on a component that cannot be updated or patched to fix security flaws or critical bugs.
CWE-221 Sibling
Information Loss or Omission
This weakness occurs when an application fails to log critical security events or records them inaccurately, which can misguide security…
CWE-372 Sibling
Incomplete Internal State Distinction
This vulnerability occurs when an application fails to accurately track its own operational state. The system incorrectly assumes it's in…
CWE-400 Sibling
Uncontrolled Resource Consumption
This vulnerability occurs when an application fails to properly manage a finite resource, allowing an attacker to exhaust it and cause a…
CWE-410 Sibling
Insufficient Resource Pool
This vulnerability occurs when a system's resource pool is too small to handle maximum usage. Attackers can exploit this by making a high…
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