CWE-756 Base Incompleto

Missing Custom Error Page

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.

Definição

What is CWE-756?

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.
When an application crashes or encounters an unexpected condition, the web server or framework often generates a default error response. These generic pages can be a goldmine for attackers, revealing stack traces, database schemas, server versions, internal file paths, or snippets of code. This exposed information significantly lowers the effort required for further exploitation, as it provides clear clues about the underlying technology and potential weaknesses. To prevent this, developers should implement a centralized error handler that intercepts all uncaught exceptions and HTTP error statuses (like 404 or 500). This handler must then respond with a consistent, branded page that informs the user a problem occurred—without any technical details—while logging the full diagnostic information securely on the server side for internal debugging. This simple practice improves both security and user experience.
Impacto no mundo real

Real-world CVEs caused by CWE-756

Ainda não há referências CVE públicas associadas a este CWE no catálogo da MITRE.

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    In the snippet below, an unchecked runtime exception thrown from within the try block may cause the container to display its default error page (which may contain a full stack trace, among other things).

  2. 2

    The mode attribute of the tag in the Web.config file defines whether custom or default error pages are used.

  3. 3

    In the following insecure ASP.NET application setting, custom error message mode is turned off. An ASP.NET error message with detailed stack trace and platform versions will be returned.

  4. 4

    A more secure setting is to set the custom error message mode for remote users only. No defaultRedirect error page is specified. The local user on the web server will see a detailed stack trace. For remote users, an ASP.NET error message with the server customError configuration setting and the platform version will be returned.

  5. 5

    Another secure option is to set the mode attribute of the tag to use a custom page as follows:

Exemplo de código vulnerável

Vulnerable Java

In the snippet below, an unchecked runtime exception thrown from within the try block may cause the container to display its default error page (which may contain a full stack trace, among other things).

Vulnerável Java 
Public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  	try {
  		...
  	} catch (ApplicationSpecificException ase) {
  		logger.error("Caught: " + ase.toString());
  	}
  }
Exemplo de código seguro

Secure ASP.NET

A more secure setting is to set the custom error message mode for remote users only. No defaultRedirect error page is specified. The local user on the web server will see a detailed stack trace. For remote users, an ASP.NET error message with the server customError configuration setting and the platform version will be returned.

Seguro ASP.NET 
<customErrors mode="RemoteOnly" />
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-756

  • 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.
Sinais de deteção

How to detect CWE-756

SAST High

Executar análise estática (SAST) na base de código à procura do padrão inseguro no fluxo de dados.

DAST Moderate

Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.

Runtime Moderate

Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.

Code review Moderate

Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-756 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-756?

This vulnerability occurs when an application fails to display its own user-friendly error pages, instead falling back to default system messages that can leak sensitive technical details.

Qual a gravidade do CWE-756?

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-756?

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

Como posso prevenir o CWE-756?

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.

Como é que o Plexicus deteta e corrige o CWE-756?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-756 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-756?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/756.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-756

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Recursos

Further reading

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