CWE-364 Base Incompleto Medium likelihood

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 corrupted through asynchronous execution.

Definição

What is CWE-364?

A signal handler race condition occurs when a program's signal handling routine is vulnerable to timing issues, allowing its state to be corrupted through asynchronous execution.
Signal handlers are inherently risky because they can interrupt a program's normal execution at any point. If a handler modifies shared resources like global variables, uses non-reentrant functions (e.g., malloc, free, printf), or is registered for multiple signals, it can corrupt memory. This happens when the handler's actions clash with operations in the main code or other handlers, leading to use-after-free, double-free, or other memory corruption vulnerabilities that attackers can exploit for denial of service or code execution. To prevent these issues, design signal handlers to be minimal and reentrant. Avoid shared state, use only async-signal-safe functions, and consider blocking (masking) other signals within the handler to ensure atomicity. For resources that must be shared, implement proper synchronization or use a flag that the main program checks safely after the signal handler returns, moving complex logic out of the handler itself.
Impacto no mundo real

Real-world CVEs caused by CWE-364

  • CVE-1999-0035

    Signal handler does not disable other signal handlers, allowing it to be interrupted, causing other functionality to access files/etc. with raised privileges

  • CVE-2001-0905

    Attacker can send a signal while another signal handler is already running, leading to crash or execution with root privileges

  • CVE-2001-1349

    unsafe calls to library functions from signal handler

  • CVE-2004-0794

    SIGURG can be used to remotely interrupt signal handler; other variants exist

  • CVE-2004-2259

    SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.

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 (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.

  2. 2

    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:

  3. 3

    - 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.

  4. 4

    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.

  5. 5

    Note that this is an adaptation of a classic example as originally presented by Michal Zalewski [REF-360]; the original example was shown to be exploitable for code execution.

Exemplo de código vulnerável

Vulnerable C

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.

Vulnerável C 
char *logMessage;
  void handler (int sigNum) {
  		syslog(LOG_NOTICE, "%s\n", logMessage);
  		free(logMessage);
```
/* artificially increase the size of the timing window to make demonstration of this weakness easier. */* 
  		
  		sleep(10);
  		exit(0);}
  
  int main (int argc, char* argv[]) {
  ```
  		logMessage = strdup(argv[1]);
```
/* Register signal handlers. */* 
  		
  		signal(SIGHUP, handler);
  		signal(SIGTERM, handler);
  		
  		 */* artificially increase the size of the timing window to make demonstration of this weakness easier. */* 
  		
  		sleep(10);}
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-364

  • Requirements Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
  • Architecture and Design Design signal handlers to only set flags, rather than perform complex functionality. These flags can then be checked and acted upon within the main program loop.
  • Implementation Only use reentrant functions within signal handlers. Also, use validation to ensure that state is consistent while performing asynchronous actions that affect the state of execution.
Sinais de deteção

How to detect CWE-364

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-364 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-364?

A signal handler race condition occurs when a program's signal handling routine is vulnerable to timing issues, allowing its state to be corrupted through asynchronous execution.

Qual a gravidade do CWE-364?

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-364?

MITRE lists the following affected platforms: C, C++.

Como posso prevenir o CWE-364?

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Design signal handlers to only set flags, rather than perform complex functionality. These flags can then be checked and acted upon within the main program loop.

Como é que o Plexicus deteta e corrige o CWE-364?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-364 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-364?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/364.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-364

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Hardware Logic Contains Race Conditions

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Race Condition within a Thread

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CWE-367 Irmão

Time-of-check Time-of-use (TOCTOU) Race Condition

This vulnerability occurs when a program verifies a resource's state (like a file's permissions or existence) but then uses it after that…

CWE-368 Irmão

Context Switching Race Condition

This vulnerability occurs when an application switches between different security contexts (like privilege levels or domains) using a…

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Race Condition During Access to Alternate Channel

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CWE-689 Irmão

Permission Race Condition During Resource Copy

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation…

CWE-415 Pode preceder

Double Free

A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.

Recursos

Further reading

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