CWE-755 Classe Incompleto Medium likelihood

Improper Handling of Exceptional Conditions

This vulnerability occurs when software fails to properly manage unexpected situations or errors, leaving it in an unstable or insecure state.

Definição

What is CWE-755?

This vulnerability occurs when software fails to properly manage unexpected situations or errors, leaving it in an unstable or insecure state.
When a program encounters something unexpected—like a failed network connection, corrupted data, or exhausted system resources—it must handle it gracefully. Improper exception handling means the software might crash, expose sensitive debugging information, or continue operating with incorrect assumptions, creating openings for attackers to exploit. To prevent this, developers should implement robust error handling that anticipates potential failure points. This includes using structured exception handling mechanisms, defining clear recovery procedures, validating all external inputs, and ensuring the application fails securely without leaking internal details that could aid an attacker.
Impacto no mundo real

Real-world CVEs caused by CWE-755

  • CVE-2023-41151

    SDK for OPC Unified Architecture (OPC UA) server has uncaught exception when a socket is blocked for writing but the server tries to send an error

  • [REF-1374]

    Chain: JavaScript-based cryptocurrency library can fall back to the insecure Math.random() function instead of reporting a failure (CWE-392), thus reducing the entropy (CWE-332) and leading to generation of non-unique cryptographic keys for Bitcoin wallets (CWE-1391)

  • CVE-2021-3011

    virtual interrupt controller in a virtualization product allows crash of host by writing a certain invalid value to a register, which triggers a fatal error instead of returning an error code

  • CVE-2008-4302

    Chain: OS kernel does not properly handle a failure of a function call (CWE-755), leading to an unlock of a resource that was not locked (CWE-832), with resultant crash.

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    The following example attempts to resolve a hostname.

  2. 2

    A DNS lookup failure will cause the Servlet to throw an exception.

  3. 3

    The following example attempts to allocate memory for a character. After the call to malloc, an if statement is used to check whether the malloc function failed.

  4. 4

    The conditional successfully detects a NULL return value from malloc indicating a failure, however it does not do anything to handle the problem. Unhandled errors may have unexpected results and may cause the program to crash or terminate.

  5. 5

    Instead, the if block should contain statements that either attempt to fix the problem or notify the user that an error has occurred and continue processing or perform some cleanup and gracefully terminate the program. The following example notifies the user that the malloc function did not allocate the required memory resources and returns an error code.

Exemplo de código vulnerável

Vulnerable Java

The following example attempts to resolve a hostname.

Vulnerável Java 
protected void doPost (HttpServletRequest req, HttpServletResponse res) throws IOException {
  	String ip = req.getRemoteAddr();
  	InetAddress addr = InetAddress.getByName(ip);
  	...
  	out.println("hello " + addr.getHostName());
  }
Exemplo de código seguro

Secure C

Instead, the if block should contain statements that either attempt to fix the problem or notify the user that an error has occurred and continue processing or perform some cleanup and gracefully terminate the program. The following example notifies the user that the malloc function did not allocate the required memory resources and returns an error code.

Seguro C 
foo=malloc(sizeof(char)); //the next line checks to see if malloc failed
  if (foo==NULL) {
  	printf("Malloc failed to allocate memory resources");
  	return -1;
  }
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-755

  • 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-755

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-755 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-755?

This vulnerability occurs when software fails to properly manage unexpected situations or errors, leaving it in an unstable or insecure state.

Qual a gravidade do CWE-755?

A MITRE classifica a probabilidade de exploração como Média — a exploração é realista mas normalmente requer condições específicas.

Que linguagens ou plataformas são afetadas pelo CWE-755?

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

Como posso prevenir o CWE-755?

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-755?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-755 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-755?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/755.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-755

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Improper Check or Handling of Exceptional Conditions

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Improper Handling of Syntactically Invalid Structure

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CWE-248 Irmão

Uncaught Exception

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CWE-391 Irmão

Unchecked Error Condition

This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By…

CWE-392 Irmão

Missing Report of Error Condition

This vulnerability occurs when a system fails to properly signal that an error has happened. Instead of returning a clear error code,…

CWE-393 Irmão

Return of Wrong Status Code

This vulnerability occurs when a function returns an inaccurate status code or value that misrepresents the actual outcome of an…

CWE-397 Irmão

Declaration of Throws for Generic Exception

This vulnerability occurs when a method is declared to throw an overly broad exception type, such as a generic 'Exception' or 'Throwable'.…

CWE-754 Irmão

Improper Check for Unusual or Exceptional Conditions

This weakness occurs when software fails to properly anticipate and handle rare or unexpected runtime situations that fall outside normal…

Recursos

Further reading

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