CWE-391 Base Incompleto Medium likelihood

Unchecked Error Condition

This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected…

Definição

What is CWE-391?

This vulnerability occurs when a program fails to properly check or handle error conditions, such as exceptions or return codes. By ignoring these failures, the software can enter an unexpected state that attackers might exploit, often without any logging or user notification.

When your code doesn't check for errors—like a failed file operation, a null pointer, or a network timeout—it continues executing as if nothing went wrong. This creates a gap between what the program assumes is true (e.g., 'the data was loaded') and reality (e.g., 'the variable is empty'), leading to crashes, data corruption, or security bypasses. Attackers can deliberately trigger these ignored errors to destabilize your application or reveal sensitive information. To prevent this, always implement robust error handling. Check return values from functions, use try-catch blocks for exceptions, and validate system call outcomes. Log all caught errors with sufficient context for debugging, and decide on safe failure modes—like rolling back transactions or terminating the session—instead of silently proceeding. This defensive practice closes a common attack vector and makes your software more resilient and observable in production.

Impacto no mundo real

Real-world CVEs caused by CWE-391

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
Identificar um caminho de código que trata input não confiável sem validação.
2
Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.
3
Entregar o payload através de um pedido normal e observar a reação da aplicação.
4
Iterar até que a resposta exponha dados, execute código do atacante ou escale privilégios.

Exemplo de código vulnerável

Vulnerable Java

The following code excerpt ignores a rarely-thrown exception from doExchange().

Vulnerável Java

try {
  	doExchange();
  }
  catch (RareException e) {
```
// this can never happen* 
  		}

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-391

Requirements The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem.
Requirements A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
Implementation Catch all relevant exceptions. This is the recommended solution. Ensure that all exceptions are handled in such a way that you can be sure of the state of your system at any given moment.

Sinais de deteção

How to detect CWE-391

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

CWE-391

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

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Perguntas frequentes

Frequently asked questions

O que é o CWE-391?

Qual a gravidade do CWE-391?

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-391?

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

Como posso prevenir o CWE-391?

The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem. A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.

Como é que o Plexicus deteta e corrige o CWE-391?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-391 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-391?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/391.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-391

CWE-754 Pai

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Reservar Pentest

Unchecked Error Condition

What is CWE-391?

Real-world CVEs caused by CWE-391

Trajeto do atacante passo a passo

Vulnerable Java

Secure pseudo

How to prevent CWE-391

How to detect CWE-391

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

Frequently asked questions

Weaknesses related to CWE-391

Improper Check for Unusual or Exceptional Conditions

Unchecked Return Value

Incorrect Check of Function Return Value

Improper Check for Dropped Privileges

Improper Validation of Integrity Check Value

Unexpected Status Code or Return Value

NULL Pointer Dereference

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`