CWE-184 Base Rascunho

Incomplete List of Disallowed Inputs

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…

Definição

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.
Vulnerability Diagram CWE-184
Incomplete Blocklist Block list <script> ✗ <SCRIPT> ? <ScRiPt> ? <img onerror> ? javascript: ? Bypass payloads <ScRiPt>…</ScRiPt> <img src=x onerror=…> SELECT/**/* FROM ..%2f..%2fetc Reaches sink XSS / SQLi / traversal still works Denylists miss case, encoding and equivalent forms — use allowlists.
Impacto no mundo real

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.

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    Identificar um caminho de código que trata input não confiável sem validação.

  2. 2

    Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.

  3. 3

    Entregar o payload através de um pedido normal e observar a reação da aplicação.

  4. 4

    Iterar até que a resposta exponha dados, execute código do atacante ou escale privilégios.

Exemplo de código vulnerável

Vulnerable Java

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

Vulnerável Java 
public String removeScriptTags(String input, String mask) {
  	return input.replaceAll("script", mask);
  }
Exemplo de código seguro

Secure pseudo

Seguro 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.
Lista de verificação de prevenção

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.
Sinais de deteção

How to detect CWE-184

Black Box

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

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-184 e abre um PR de correção em menos de 60 segundos.

O Codex Remedium analisa cada commit, identifica esta fraqueza exata e entrega um pull request pronto para revisão com o patch. Sem tickets. Sem transferências.

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Perguntas frequentes

Frequently asked questions

O que é o 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.

Qual a gravidade do CWE-184?

A MITRE não publicou uma classificação de probabilidade de exploração para esta fraqueza. Trate-a como impacto médio até o seu modelo de ameaças provar o contrário.

Que linguagens ou plataformas são afetadas pelo CWE-184?

A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.

Como posso prevenir o 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.

Como é que o Plexicus deteta e corrige o CWE-184?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-184 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.

Onde posso saber mais sobre o CWE-184?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/184.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

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Recursos

Further reading

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