CWE-479 Variante Borrador Low likelihood

Signal Handler Use of a Non-reentrant Function

This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory…

Definición

What is CWE-479?

This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory and crash your program or create security weaknesses.
Non-reentrant functions rely on global data or static memory to do their work. When a signal interrupts such a function and the handler calls the same function again, both invocations compete for and corrupt that shared state. Common examples include `malloc()`, `free()`, and `syslog()`, which use internal scratch space or metadata to track operations. This corruption can leave your application in an unpredictable and potentially exploitable state. As a developer, you must ensure that only async-signal-safe functions are called from within a signal handler. The POSIX standard defines a specific list of these safe functions. Calling anything outside this list, especially standard library functions that manage memory or perform I/O, introduces this risk of re-entrancy corruption which can lead to denial of service or, in worst cases, allow an attacker to execute arbitrary code.
Impacto en el mundo real

Real-world CVEs caused by CWE-479

  • CVE-2005-0893

    signal handler calls function that ultimately uses malloc()

  • CVE-2004-2259

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

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 1

    Identifica una ruta de código que maneje entrada no confiable sin validación.

  2. 2

    Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.

  3. 3

    Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.

  4. 4

    Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.

Ejemplo de código vulnerable

Vulnerable C

In this example, a signal handler uses syslog() to log a message:

Vulnerable C 
char *message;
  void sh(int dummy) {
  	syslog(LOG_NOTICE,"%s\n",message);
  	sleep(10);
  	exit(0);
  }
  int main(int argc,char* argv[]) {
  	...
  	signal(SIGHUP,sh);
  	signal(SIGTERM,sh);
  	sleep(10);
  	exit(0);
  }
  	If the execution of the first call to the signal handler is suspended after invoking syslog(), and the signal handler is called a second time, the memory allocated by syslog() enters an undefined, and possibly, exploitable state.
Ejemplo 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 prevención

How to prevent CWE-479

  • Requirements Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness.
  • Architecture and Design Design signal handlers to only set flags rather than perform complex functionality.
  • Implementation Ensure that non-reentrant functions are not found in signal handlers.
  • Implementation Use sanity checks to reduce the timing window for exploitation of race conditions. This is only a partial solution, since many attacks might fail, but other attacks still might work within the narrower window, even accidentally.
Señales de detección

How to detect CWE-479

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.)

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-479 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-479?

This vulnerability occurs when a signal handler in your code calls a function that is not safe to re-enter. If that function is interrupted and called again before it finishes, it can corrupt memory and crash your program or create security weaknesses.

¿Qué gravedad tiene CWE-479?

MITRE califica la probabilidad de explotación como Baja — la explotación es poco frecuente, pero la debilidad debe corregirse cuando se descubra.

¿Qué lenguajes o plataformas se ven afectados por CWE-479?

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

¿Cómo puedo prevenir CWE-479?

Require languages or libraries that provide reentrant functionality, or otherwise make it easier to avoid this weakness. Design signal handlers to only set flags rather than perform complex functionality.

¿Cómo detecta y corrige Plexicus CWE-479?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-479 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.

¿Dónde puedo aprender más sobre CWE-479?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/479.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-479

CWE-828 Padre

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…

CWE-123 Puede preceder

Write-what-where Condition

A write-what-where condition occurs when an attacker can control both the data written and the exact memory location where it's written,…

Recursos

Further reading

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