Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
Home > CWE List > CWE- Individual Dictionary Definition (3.0)  

CWE-400: Uncontrolled Resource Consumption ('Resource Exhaustion')

Weakness ID: 400
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software does not properly restrict the size or amount of resources that are requested or influenced by an actor, which can be used to consume more resources than intended.
+ Extended Description

Limited resources include memory, file system storage, database connection pool entries, or CPU. If an attacker can trigger the allocation of these limited resources, but the number or size of the resources is not controlled, then the attacker could cause a denial of service that consumes all available resources. This would prevent valid users from accessing the software, and it could potentially have an impact on the surrounding environment. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system.

Resource exhaustion problems have at least two common causes:

  • Error conditions and other exceptional circumstances
  • Confusion over which part of the program is responsible for releasing the resource
+ 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 "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
ParentOfBaseBase769Uncontrolled File Descriptor Consumption
+ 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.


Class: Language-Independent (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: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory); DoS: Resource Consumption (Other)

The most common result of resource exhaustion is denial of service. The software may slow down, crash due to unhandled errors, or lock out legitimate users.
Access Control

Technical Impact: Bypass Protection Mechanism; Other

In some cases it may be possible to force the software to "fail open" in the event of resource exhaustion. The state of the software -- and possibly the security functionality - may then be compromised.
+ Likelihood Of Exploit
+ Demonstrative Examples

Example 1

The following example demonstrates the weakness.

(bad code)
Example Language: Java 
class Worker implements Executor {
public void execute(Runnable r) {

try {

catch (InterruptedException ie) {
// postpone response



public Worker(Channel ch, int nworkers) {


protected void activate() {

Runnable loop = new Runnable() {

public void run() {

try {
for (;;) {
Runnable r = ...;;


catch (InterruptedException ie) {



new Thread(loop).start();



There are no limits to runnables. Potentially an attacker could cause resource problems very quickly.

Example 2

This code allocates a socket and forks each time it receives a new connection.

(bad code)
Example Language:
sock=socket(AF_INET, SOCK_STREAM, 0);
while (1) {
newsock=accept(sock, ...);
printf("A connection has been accepted\n");
pid = fork();


The program does not track how many connections have been made, and it does not limit the number of connections. Because forking is a relatively expensive operation, an attacker would be able to cause the system to run out of CPU, processes, or memory by making a large number of connections. Alternatively, an attacker could consume all available connections, preventing others from accessing the system remotely.

Example 3

In the following example a server socket connection is used to accept a request to store data on the local file system using a specified filename. The method openSocketConnection establishes a server socket to accept requests from a client. When a client establishes a connection to this service the getNextMessage method is first used to retrieve from the socket the name of the file to store the data, the openFileToWrite method will validate the filename and open a file to write to on the local file system. The getNextMessage is then used within a while loop to continuously read data from the socket and output the data to the file until there is no longer any data from the socket.

(bad code)
Example Language:
int writeDataFromSocketToFile(char *host, int port)

char filename[FILENAME_SIZE];
char buffer[BUFFER_SIZE];
int socket = openSocketConnection(host, port);

if (socket < 0) {
printf("Unable to open socket connection");

if (getNextMessage(socket, filename, FILENAME_SIZE) > 0) {
if (openFileToWrite(filename) > 0) {
while (getNextMessage(socket, buffer, BUFFER_SIZE) > 0){
if (!(writeToFile(buffer) > 0))





This example creates a situation where data can be dumped to a file on the local file system without any limits on the size of the file. This could potentially exhaust file or disk resources and/or limit other clients' ability to access the service.

Example 4

In the following example, the processMessage method receives a two dimensional character array containing the message to be processed. The two-dimensional character array contains the length of the message in the first character array and the message body in the second character array. The getMessageLength method retrieves the integer value of the length from the first character array. After validating that the message length is greater than zero, the body character array pointer points to the start of the second character array of the two-dimensional character array and memory is allocated for the new body character array.

(bad code)
Example Language:
/* process message accepts a two-dimensional character array of the form [length][body] containing the message to be processed */
int processMessage(char **message)
char *body;

int length = getMessageLength(message[0]);

if (length > 0) {
body = &message[1][0];

else {
printf("Unable to process message; invalid message length");



This example creates a situation where the length of the body character array can be very large and will consume excessive memory, exhausting system resources. This can be avoided by restricting the length of the second character array with a maximum length check

Also, consider changing the type from 'int' to 'unsigned int', so that you are always guaranteed that the number is positive. This might not be possible if the protocol specifically requires allowing negative values, or if you cannot control the return value from getMessageLength(), but it could simplify the check to ensure the input is positive, and eliminate other errors such as signed-to-unsigned conversion errors (CWE-195) that may occur elsewhere in the code.

(good code)
Example Language:
unsigned int length = getMessageLength(message[0]);
if ((length > 0) && (length < MAX_LENGTH)) {...}

Example 5

In the following example, a server object creates a server socket and accepts client connections to the socket. For every client connection to the socket a separate thread object is generated using the ClientSocketThread class that handles request made by the client through the socket.

(bad code)
Example Language: Java 
public void acceptConnections() {
try {
ServerSocket serverSocket = new ServerSocket(SERVER_PORT);
int counter = 0;
boolean hasConnections = true;
while (hasConnections) {
Socket client = serverSocket.accept();
Thread t = new Thread(new ClientSocketThread(client));
t.setName(client.getInetAddress().getHostName() + ":" + counter++);


} catch (IOException ex) {...}


In this example there is no limit to the number of client connections and client threads that are created. Allowing an unlimited number of client connections and threads could potentially overwhelm the system and system resources.

The server should limit the number of client connections and the client threads that are created. This can be easily done by creating a thread pool object that limits the number of threads that are generated.

(good code)
Example Language: Java 
public static final int SERVER_PORT = 4444;
public static final int MAX_CONNECTIONS = 10;

public void acceptConnections() {
try {
ServerSocket serverSocket = new ServerSocket(SERVER_PORT);
int counter = 0;
boolean hasConnections = true;
while (hasConnections) {
hasConnections = checkForMoreConnections();
Socket client = serverSocket.accept();
Thread t = new Thread(new ClientSocketThread(client));
t.setName(client.getInetAddress().getHostName() + ":" + counter++);
ExecutorService pool = Executors.newFixedThreadPool(MAX_CONNECTIONS);


} catch (IOException ex) {...}

+ Observed Examples
Product allows attackers to cause a crash via a large number of connections.
Malformed request triggers uncontrolled recursion, leading to stack exhaustion.
Chain: memory leak (CWE-404) leads to resource exhaustion.
Driver does not use a maximum width when invoking sscanf style functions, causing stack consumption.
Large integer value for a length property in an object causes a large amount of memory allocation.
Web application firewall consumes excessive memory when an HTTP request contains a large Content-Length value but no POST data.
Product allows exhaustion of file descriptors when processing a large number of TCP packets.
Communication product allows memory consumption with a large number of SIP requests, which cause many sessions to be created.
TCP implementation allows attackers to consume CPU and prevent new connections using a TCP SYN flood attack.
Port scan triggers CPU consumption with processes that attempt to read data from closed sockets.
Product allows attackers to cause a denial of service via a large number of directives, each of which opens a separate window.
Product allows resource exhaustion via a large number of calls that do not complete a 3-way handshake.
Mail server does not properly handle deeply nested multipart MIME messages, leading to stack exhaustion.
Chain: anti-virus product encounters a malformed file but returns from a function without closing a file descriptor (CWE-775) leading to file descriptor consumption (CWE-400) and failed scans.
+ Potential Mitigations

Phase: Architecture and Design

Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.

Phase: Architecture and Design

Mitigation of resource exhaustion attacks requires that the target system either:

  • recognizes the attack and denies that user further access for a given amount of time, or
  • uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed.

The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.

The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.

Phase: Architecture and Design

Ensure that protocols have specific limits of scale placed on them.

Phase: Implementation

Ensure that all failures in resource allocation place the system into a safe posture.
+ Detection Methods

Automated Static Analysis

Automated static analysis typically has limited utility in recognizing resource exhaustion problems, except for program-independent system resources such as files, sockets, and processes. For system resources, automated static analysis may be able to detect circumstances in which resources are not released after they have expired. Automated analysis of configuration files may be able to detect settings that do not specify a maximum value.

Automated static analysis tools will not be appropriate for detecting exhaustion of custom resources, such as an intended security policy in which a bulletin board user is only allowed to make a limited number of posts per day.

Effectiveness: Limited

Automated Dynamic Analysis

Certain automated dynamic analysis techniques may be effective in spotting resource exhaustion problems, especially with resources such as processes, memory, and connections. The technique may involve generating a large number of requests to the software within a short time frame.

Effectiveness: Moderate


While fuzzing is typically geared toward finding low-level implementation bugs, it can inadvertently find resource exhaustion problems. This can occur when the fuzzer generates a large number of test cases but does not restart the targeted software in between test cases. If an individual test case produces a crash, but it does not do so reliably, then an inability to handle resource exhaustion may be the cause.

Effectiveness: Opportunistic

+ 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


Database queries that take a long time to process are good DoS targets. An attacker would have to write a few lines of Perl code to generate enough traffic to exceed the site's ability to keep up. This would effectively prevent authorized users from using the site at all. Resources can be exploited simply by ensuring that the target machine must do much more work and consume more resources in order to service a request than the attacker must do to initiate a request.

A prime example of this can be found in old switches that were vulnerable to "macof" attacks (so named for a tool developed by Dugsong). These attacks flooded a switch with random IP and MAC address combinations, therefore exhausting the switch's cache, which held the information of which port corresponded to which MAC addresses. Once this cache was exhausted, the switch would fail in an insecure way and would begin to act simply as a hub, broadcasting all traffic on all ports and allowing for basic sniffing attacks.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPResource exhaustion (file descriptor, disk space, sockets, ...)
OWASP Top Ten 2004A9CWE More SpecificDenial of Service
WASC10Denial of Service
WASC41XML Attribute Blowup
CERT Java Secure CodingSER12-JAvoid memory and resource leaks during serialization
CERT Java Secure CodingMSC05-JDo not exhaust heap space
Software Fault PatternsSFP13Unrestricted Consumption
+ References
[REF-386] Joao Antunes, Nuno Ferreira Neves and Paulo Verissimo. "Detection and Prediction of Resource-Exhaustion Vulnerabilities". Proceedings of the IEEE International Symposium on Software Reliability Engineering (ISSRE). 2008-11. <>.
[REF-387] D.J. Bernstein. "Resource exhaustion". <>.
[REF-388] Pascal Meunier. "Resource exhaustion". Secure Programming Educational Material. 2004. <>.
[REF-112] Michael Howard and David LeBlanc. "Writing Secure Code". Chapter 17, "Protecting Against Denial of Service Attacks" Page 517. 2nd Edition. Microsoft. 2002.
+ Content History
Submission DateSubmitterOrganization
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITRE
updated Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Description, Name, Relationships
2009-01-12CWE Content TeamMITRE
updated Description
2009-05-27CWE Content TeamMITRE
updated Name, Relationships
2009-07-27CWE Content TeamMITRE
updated Description, Relationships
2009-10-29CWE Content TeamMITRE
updated Relationships
2009-12-28CWE Content TeamMITRE
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, Observed_Examples, Other_Notes, Potential_Mitigations, References
2010-02-16CWE Content TeamMITRE
updated Detection_Factors, Potential_Mitigations, References, Taxonomy_Mappings
2010-04-05CWE Content TeamMITRE
updated Related_Attack_Patterns
2010-06-21CWE Content TeamMITRE
updated Description
2010-09-27CWE Content TeamMITRE
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITRE
updated Demonstrative_Examples, Related_Attack_Patterns, Relationships, Taxonomy_Mappings
2013-07-17CWE Content TeamMITRE
updated Relationships
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings
2015-12-07CWE Content TeamMITRE
updated Related_Attack_Patterns, Relationships
2017-01-19CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Demonstrative_Examples, Likelihood_of_Exploit, Potential_Mitigations, References, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-10-14Resource Exhaustion
2009-05-27Uncontrolled Resource Consumption (aka 'Resource Exhaustion')

More information is available — Please select a different filter.
Page Last Updated: January 18, 2018