CWE-831 Variante Incompleto

Signal Handler Function Associated with Multiple Signals

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.

Definição

What is CWE-831?

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.
When the same function handles multiple signals, an attacker can exploit timing issues by sending a second signal while the handler is still processing the first. If the handler uses shared resources like global variables or non-reentrant functions, this interruption can corrupt program state, potentially leading to crashes, denial of service, or even code execution. Even without classic race conditions, this pattern creates risk. Attackers can trigger the handler multiple times by sending different signals sequentially, causing unintended side effects. This is especially dangerous for handlers designed to run only once, as forced re-execution can bypass security controls or destabilize the application.
Impacto no mundo real

Real-world CVEs caused by CWE-831

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

    This code registers the same signal handler function with two different signals.

  2. 2

    This code registers the same signal handler function with two different signals (CWE-831). If those signals are sent to the process, the handler creates a log message (specified in the first argument to the program) and exits.

  3. 3

    The handler function uses global state (globalVar and logMessage), and it can be called by both the SIGHUP and SIGTERM signals. An attack scenario might follow these lines:

  4. 4

    - The program begins execution, initializes logMessage, and registers the signal handlers for SIGHUP and SIGTERM. - The program begins its "normal" functionality, which is simplified as sleep(), but could be any functionality that consumes some time. - The attacker sends SIGHUP, which invokes handler (call this "SIGHUP-handler"). - SIGHUP-handler begins to execute, calling syslog(). - syslog() calls malloc(), which is non-reentrant. malloc() begins to modify metadata to manage the heap. - The attacker then sends SIGTERM. - SIGHUP-handler is interrupted, but syslog's malloc call is still executing and has not finished modifying its metadata. - The SIGTERM handler is invoked. - SIGTERM-handler records the log message using syslog(), then frees the logMessage variable.

  5. 5

    At this point, the state of the heap is uncertain, because malloc is still modifying the metadata for the heap; the metadata might be in an inconsistent state. The SIGTERM-handler call to free() is assuming that the metadata is inconsistent, possibly causing it to write data to the wrong location while managing the heap. The result is memory corruption, which could lead to a crash or even code execution, depending on the circumstances under which the code is running.

Exemplo de código vulnerável

Vulnerable C

This code registers the same signal handler function with two different signals.

Vulnerável C 
void handler (int sigNum) {
  	...
  }
  int main (int argc, char* argv[]) {
  	signal(SIGUSR1, handler)
  	signal(SIGUSR2, handler)
  }
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-831

  • 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-831

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-831 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-831?

This vulnerability occurs when a single function is registered to handle multiple different operating system signals, creating potential race conditions if that function isn't carefully designed.

Qual a gravidade do CWE-831?

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-831?

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

Como posso prevenir o CWE-831?

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-831?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-831 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-831?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/831.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-831

CWE-364 Pai

Signal Handler Race Condition

A signal handler race condition occurs when a program's signal handling routine is vulnerable to timing issues, allowing its state to be…

CWE-432 Irmão

Dangerous Signal Handler not Disabled During Sensitive Operations

This vulnerability occurs when a program's signal handler, which shares resources like global variables with other handlers, can be…

CWE-828 Irmão

Signal Handler with Functionality that is not Asynchronous-Safe

This weakness occurs when a program's signal handler contains code that is not asynchronous-safe. This means the handler can be…

Recursos

Further reading

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