CWE-835 Base Incomplet

Loop with Unreachable Exit Condition ('Infinite Loop')

An infinite loop occurs when a program's iteration logic contains an exit condition that can never be satisfied, causing the loop to run indefinitely and consume system resources.

Définition

What is CWE-835?

An infinite loop occurs when a program's iteration logic contains an exit condition that can never be satisfied, causing the loop to run indefinitely and consume system resources.
This vulnerability typically stems from flawed loop logic where the condition for termination is incorrectly defined. Common causes include using a loop counter that never updates, checking against a variable that doesn't change within the loop body, or creating circular dependencies where the exit state becomes mathematically impossible to reach. Developers might introduce these errors through simple typos, incorrect operator usage, or misunderstanding how loop variables interact with other parts of the code. When an infinite loop executes, it can lead to denial of service by exhausting CPU cycles, memory, or other finite resources, potentially freezing the application or the entire system. To prevent this, always validate that loop control variables are properly modified inside the loop and that exit conditions are based on values that will eventually change. Using timeouts, circuit breakers, or defensive programming techniques like maximum iteration limits can provide safety nets for unexpected logic errors.
Vulnerability Diagram CWE-835
Infinite Loop while (cond) // cond never updates repeat forever CPU 100% — process unresponsive other threads / requests starve Loop exit condition can never become false.
Impact réel

Real-world CVEs caused by CWE-835

  • CVE-2022-22224

    Chain: an operating system does not properly process malformed Open Shortest Path First (OSPF) Type/Length/Value Identifiers (TLV) (CWE-703), which can cause the process to enter an infinite loop (CWE-835)

  • CVE-2022-25304

    A Python machine communication platform did not account for receiving a malformed packet with a null size, causing the receiving function to never update the message buffer and be caught in an infinite loop.

  • CVE-2011-1027

    Chain: off-by-one error (CWE-193) leads to infinite loop (CWE-835) using invalid hex-encoded characters.

  • CVE-2011-1142

    Chain: self-referential values in recursive definitions lead to infinite loop.

  • CVE-2011-1002

    NULL UDP packet is never cleared from a queue, leading to infinite loop.

  • CVE-2006-6499

    Chain: web browser crashes due to infinite loop - "bad looping logic [that relies on] floating point math [CWE-1339] to exit the loop [CWE-835]"

  • CVE-2010-4476

    Floating point conversion routine cycles back and forth between two different values.

  • CVE-2010-4645

    Floating point conversion routine cycles back and forth between two different values.

Comment les attaquants l'exploitent

Parcours de l'attaquant étape par étape

  1. 1

    In the following code the method processMessagesFromServer attempts to establish a connection to a server and read and process messages from the server. The method uses a do/while loop to continue trying to establish the connection to the server when an attempt fails.

  2. 2

    However, this will create an infinite loop if the server does not respond. This infinite loop will consume system resources and can be used to create a denial of service attack. To resolve this a counter should be used to limit the number of attempts to establish a connection to the server, as in the following code.

  3. 3

    For this example, the method isReorderNeeded is part of a bookstore application that determines if a particular book needs to be reordered based on the current inventory count and the rate at which the book is being sold.

  4. 4

    However, the while loop will become an infinite loop if the rateSold input parameter has a value of zero since the inventoryCount will never fall below the minimumCount. In this case the input parameter should be validated to ensure that a value of zero does not cause an infinite loop, as in the following code.

Exemple de code vulnérable

Vulnerable C

In the following code the method processMessagesFromServer attempts to establish a connection to a server and read and process messages from the server. The method uses a do/while loop to continue trying to establish the connection to the server when an attempt fails.

Vulnérable C 
int processMessagesFromServer(char *hostaddr, int port) {
  		...
  		int servsock;
  		int connected;
  		struct sockaddr_in servaddr;
```
// create socket to connect to server* 
  		servsock = socket( AF_INET, SOCK_STREAM, 0);
  		memset( &servaddr, 0, sizeof(servaddr));
  		servaddr.sin_family = AF_INET;
  		servaddr.sin_port = htons(port);
  		servaddr.sin_addr.s_addr = inet_addr(hostaddr);
  		
  		do {
  		```
```
// establish connection to server* 
  				connected = connect(servsock, (struct sockaddr *)&servaddr, sizeof(servaddr));
  				
  				
  				 *// if connected then read and process messages from server* 
  				if (connected > -1) {
  				```
```
// read and process messages* 
  						...}
  				
  		
  		 *// keep trying to establish connection to the server* 
  		} while (connected < 0);
  		
  		
  		 *// close socket and return success or failure* 
  		...}
Exemple de code sécurisé

Secure C

However, this will create an infinite loop if the server does not respond. This infinite loop will consume system resources and can be used to create a denial of service attack. To resolve this a counter should be used to limit the number of attempts to establish a connection to the server, as in the following code.

Sécurisé C 
int processMessagesFromServer(char *hostaddr, int port) {
  		...
```
// initialize number of attempts counter* 
  		int count = 0;
  		do {
  		```
```
// establish connection to server* 
  				connected = connect(servsock, (struct sockaddr *)&servaddr, sizeof(servaddr));
  				
  				
  				 *// increment counter* 
  				count++;
  				
  				
  				 *// if connected then read and process messages from server* 
  				if (connected > -1) {
  				```
```
// read and process messages* 
  						...}
  				
  		
  		 *// keep trying to establish connection to the server* 
  		
  		
  		 *// up to a maximum number of attempts* 
  		} while (connected < 0 && count < MAX_ATTEMPTS);
  		
  		
  		 *// close socket and return success or failure* 
  		...}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Liste de contrôle de prévention

How to prevent CWE-835

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Signaux de détection

How to detect CWE-835

SAST High

Exécuter une analyse statique (SAST) sur le code source à la recherche du motif non sécurisé dans le flux de données.

DAST Moderate

Exécuter des tests de sécurité applicative dynamique (DAST) contre le point de terminaison en ligne.

Runtime Moderate

Surveiller les journaux runtime pour détecter des traces d'exception inhabituelles, des entrées malformées ou des tentatives de contournement d'autorisation.

Code review Moderate

Revue de code : signaler tout nouveau code qui traite les entrées de cette surface sans utiliser les helpers du framework validés.

Correction automatique Plexicus

Plexicus détecte automatiquement CWE-835 et ouvre une PR de correction en moins de 60 secondes.

Codex Remedium analyse chaque commit, identifie cette faiblesse précise et livre une pull request prête à être relue avec le correctif. Pas de tickets. Pas de transferts.

Obtenir une démo Essayer Plexicus gratuitement
Questions fréquentes

Frequently asked questions

Qu'est-ce que CWE-835 ?

An infinite loop occurs when a program's iteration logic contains an exit condition that can never be satisfied, causing the loop to run indefinitely and consume system resources.

Quelle est la gravité de CWE-835 ?

MITRE n'a pas publié de note de probabilité d'exploitation pour cette faiblesse. Traitez-la comme un impact moyen jusqu'à ce que votre modèle de menace prouve le contraire.

Quels langages ou plateformes sont affectés par CWE-835 ?

MITRE n'a pas spécifié les plateformes affectées pour ce CWE — il peut s'appliquer à la plupart des stacks applicatives.

Comment puis-je prévenir CWE-835 ?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

Comment Plexicus détecte et corrige CWE-835 ?

Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-835 à chaque commit. Lorsqu'une correspondance est trouvée, notre agent Codex Remedium ouvre une PR de correction avec le code corrigé, les tests et un résumé d'une ligne pour le relecteur.

Où puis-je en savoir plus sur CWE-835 ?

MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/835.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.

Faiblesses associées

Weaknesses related to CWE-835

CWE-834 Parent

Excessive Iteration

This vulnerability occurs when a program runs a loop too many times because it lacks proper limits on its iterations.

CWE-1322 Frère

Use of Blocking Code in Single-threaded, Non-blocking Context

This vulnerability occurs when an application designed to be single-threaded and non-blocking, for performance and scalability,…

CWE-674 Frère

Uncontrolled Recursion

This vulnerability occurs when an application fails to limit how deeply a function can call itself. Without proper controls, this…

Ressources

Further reading

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