Ejecuta análisis estático (SAST) sobre el código buscando el patrón inseguro en el flujo de datos.
CWE-828 Variante Incompleto
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 interrupted or can corrupt shared data, leading to unpredictable…
Definición
What is CWE-828?
This weakness occurs when a program's signal handler contains code that is not asynchronous-safe. This means the handler can be interrupted or can corrupt shared data, leading to unpredictable program behavior.
Signal handlers interrupt your program's normal flow to process events. If these handlers use global variables, call non-reentrant functions like malloc(), or modify shared state, they can corrupt memory or program logic when interrupted. This corruption often creates race conditions, making your application vulnerable to crashes (denial of service) or, in some cases, allowing an attacker to execute arbitrary code.
A common pitfall is writing handlers that assume they run only once, but signals can fire repeatedly or share the same handler. If your main code and the signal handler both access the same data, an incoming signal can leave that data in a broken, inconsistent state. Since very few functions are truly reentrant, you must carefully design handlers to use only asynchronous-safe operations to maintain system stability.
Impacto en el mundo real
Real-world CVEs caused by CWE-828
-
Signal handler uses functions that ultimately call the unsafe syslog/malloc/s*printf, leading to denial of service via multiple login attempts
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Chain: Signal handler contains too much functionality (CWE-828), introducing a race condition (CWE-362) that leads to a double free (CWE-415).
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unsafe calls to library functions from signal handler
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SIGURG can be used to remotely interrupt signal handler; other variants exist.
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SIGCHLD signal to FTP server can cause crash under heavy load while executing non-reentrant functions like malloc/free.
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SIGCHLD not blocked in a daemon loop while counter is modified, causing counter to get out of sync.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 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
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
- 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
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
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.
Ejemplo de código vulnerable
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.
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);} 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-828
- Implementation / Architecture and Design Eliminate the usage of non-reentrant functionality inside of signal handlers. This includes replacing all non-reentrant library calls with reentrant calls. Note: This will not always be possible and may require large portions of the product to be rewritten or even redesigned. Sometimes reentrant-safe library alternatives will not be available. Sometimes non-reentrant interaction between the state of the system and the signal handler will be required by design.
- Implementation Where non-reentrant functionality must be leveraged within a signal handler, be sure to block or mask signals appropriately. This includes blocking other signals within the signal handler itself that may also leverage the functionality. It also includes blocking all signals reliant upon the functionality when it is being accessed or modified by the normal behaviors of the product.
Señales de detección
How to detect CWE-828
Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.
Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.
Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.
Plexicus detecta automáticamente CWE-828 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.
Preguntas frecuentes ¿Qué es CWE-828?
¿Qué gravedad tiene CWE-828?
¿Qué lenguajes o plataformas se ven afectados por CWE-828?
¿Cómo puedo prevenir CWE-828?
¿Cómo detecta y corrige Plexicus CWE-828?
¿Dónde puedo aprender más sobre CWE-828?
Frequently asked questions
¿Qué es CWE-828?
This weakness occurs when a program's signal handler contains code that is not asynchronous-safe. This means the handler can be interrupted or can corrupt shared data, leading to unpredictable program behavior.
¿Qué gravedad tiene CWE-828?
MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.
¿Qué lenguajes o plataformas se ven afectados por CWE-828?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-828?
Eliminate the usage of non-reentrant functionality inside of signal handlers. This includes replacing all non-reentrant library calls with reentrant calls. Note: This will not always be possible and may require large portions of the product to be rewritten or even redesigned. Sometimes reentrant-safe library alternatives will not be available. Sometimes non-reentrant interaction between the state of the system and the signal handler will be required by design. Where non-reentrant functionality…
¿Cómo detecta y corrige Plexicus CWE-828?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-828 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-828?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/828.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-828
CWE-364 Padre
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 Hermano
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-831 Hermano
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…
CWE-479 Hijo
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…
Recursos
Further reading
- MITRE — CWE-828 oficial https://cwe.mitre.org/data/definitions/828.html
- Delivering Signals for Fun and Profit https://lcamtuf.coredump.cx/signals.txt
- Race Condition: Signal Handling https://vulncat.fortify.com/en/detail?id=desc.structural.cpp.race_condition_signal_handling#:~:text=Signal%20handling%20race%20conditions%20can,installed%20to%20handle%20multiple%20signals.s
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