CWE-184: Incomplete List of Disallowed Inputs

Définition

What is CWE-184?

This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but that list is missing critical entries. Attackers can bypass the protection by using variations or inputs the developers didn't anticipate.

Denylist-based security is fundamentally fragile because it requires developers to predict and block every possible bad input. This approach often fails against sophisticated attacks, as attackers constantly evolve their techniques to use new encodings, character sequences, or command variations that aren't on the list. Relying solely on a denylist creates a false sense of security and is difficult to maintain over time. For stronger protection, prioritize 'allowlisting' (only permitting known-good patterns) over denylisting. If a denylist is unavoidable, complement it with other defenses like strict input validation, output encoding, and security libraries designed to handle the specific threat. Always assume your denylist is incomplete and design your system to fail safely when an unexpected input is encountered.

Impact réel

Real-world CVEs caused by CWE-184

CVE-2024-4315

Chain: API for text generation using Large Language Models (LLMs) does not include the "\" Windows folder separator in its denylist (CWE-184) when attempting to prevent Local File Inclusion via path traversal (CWE-22), allowing deletion of arbitrary files on Windows systems.
CVE-2008-2309

product uses a denylist to identify potentially dangerous content, allowing attacker to bypass a warning
CVE-2005-2782

PHP remote file inclusion in web application that filters "http" and "https" URLs, but not "ftp".
CVE-2004-0542

Programming language does not filter certain shell metacharacters in Windows environment.
CVE-2004-0595

XSS filter doesn't filter null characters before looking for dangerous tags, which are ignored by web browsers. MIE and validate-before-cleanse.
CVE-2005-3287

Web-based mail product doesn't restrict dangerous extensions such as ASPX on a web server, even though others are prohibited.
CVE-2004-2351

Resultant XSS when only and are checked.
CVE-2005-2959

Privileged program does not clear sensitive environment variables that are used by bash. Overlaps multiple interpretation error.

Comment les attaquants l'exploitent

Parcours de l'attaquant étape par étape

1
Identifier un chemin de code qui traite des entrées non fiables sans validation.
2
Élaborer une charge utile qui exploite le comportement non sécurisé — injection, traversal, débordement ou abus de logique.
3
Délivrer la charge utile via une requête normale et observer la réaction de l'application.
4
Itérer jusqu'à ce que la réponse divulgue des données, exécute le code de l'attaquant ou élève les privilèges.

Exemple de code vulnérable

Vulnerable Java

The following code attempts to stop XSS attacks by removing all occurences of "script" in an input string.

Vulnérable Java

public String removeScriptTags(String input, String mask) {
  	return input.replaceAll("script", mask);
  }

Exemple de code sécurisé

Secure pseudo

Sécurisé pseudo

// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}

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-184

Implementation Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity. Ensure that you are using other protection mechanisms that only identify "good" input - such as lists of allowed inputs - and ensure that you are properly encoding your outputs.

Signaux de détection

How to detect CWE-184

Black Box

Exploitation of a vulnerability with commonly-used manipulations might fail, but minor variations might succeed.

CWE-184

Don't catalog this weakness. Prove it's reachable.

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Questions fréquentes

Frequently asked questions

Qu'est-ce que CWE-184 ?

This vulnerability occurs when a security filter or validation mechanism relies on a 'denylist'—a predefined list of forbidden inputs—but that list is missing critical entries. Attackers can bypass the protection by using variations or inputs the developers didn't anticipate.

Quelle est la gravité de CWE-184 ?

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-184 ?

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-184 ?

Do not rely exclusively on detecting disallowed inputs. There are too many variants to encode a character, especially when different environments are used, so there is a high likelihood of missing some variants. Only use detection of disallowed inputs as a mechanism for detecting suspicious activity. Ensure that you are using other protection mechanisms that only identify "good" input - such as lists of allowed inputs - and ensure that you are properly encoding your outputs.

Comment Plexicus détecte et corrige CWE-184 ?

Le moteur SAST de Plexicus reconnaît la signature de flux de données de CWE-184 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-184 ?

MITRE publie la définition canonique à https://cwe.mitre.org/data/definitions/184.html. Vous pouvez également consulter la documentation OWASP et NIST pour des conseils adjacents.

Faiblesses associées

Weaknesses related to CWE-184

CWE-693 Parent

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Incomplete List of Disallowed Inputs

What is CWE-184?

Real-world CVEs caused by CWE-184

Parcours de l'attaquant étape par étape

Vulnerable Java

Secure pseudo

How to prevent CWE-184

How to detect CWE-184

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-184

Protection Mechanism Failure

Inadequate Detection or Handling of Adversarial Input Perturbations in Automated Recognition Mechanism

Semiconductor Defects in Hardware Logic with Security-Sensitive Implications

Incorrect Selection of Fuse Values

Product Released in Non-Release Configuration

Missing Protection Against Hardware Reverse Engineering Using Integrated Circuit (IC) Imaging Techniques

Public Key Re-Use for Signing both Debug and Production Code

Missing Support for Security Features in On-chip Fabrics or Buses

Improper Protection against Electromagnetic Fault Injection (EM-FI)

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`