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-479 Variante Borrador
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
-
signal handler calls function that ultimately uses malloc()
-
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
Identifica una ruta de código que maneje entrada no confiable sin validación.
- 2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
- 3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
- 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:
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
// 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
CWE-479
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Preguntas frecuentes ¿Qué es CWE-479?
¿Qué gravedad tiene CWE-479?
¿Qué lenguajes o plataformas se ven afectados por CWE-479?
¿Cómo puedo prevenir CWE-479?
¿Cómo detecta y corrige Plexicus CWE-479?
¿Dónde puedo aprender más sobre CWE-479?
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,…
¿Listo para validar lo que importa?
Listo para validar lo que importa.
Plexicus es Proof-Driven AppSec: hallazgos validados, comprensión contextual y remediación revisada — anclada en evidencia, acotada contigo.