CWE-768 Variante Incompleto Low likelihood

Incorrect Short Circuit Evaluation

This vulnerability occurs when a program's conditional statement uses short-circuit evaluation (where later parts of an AND/OR check are skipped if the outcome is already determined), and the…

Definición

What is CWE-768?

This vulnerability occurs when a program's conditional statement uses short-circuit evaluation (where later parts of an AND/OR check are skipped if the outcome is already determined), and the skipped portions contain code that changes the program's state. Because these side effects—like updating a variable, checking a permission, or logging an event—are never executed, the application can enter an unexpected and potentially insecure state.
Short-circuit evaluation is a standard programming feature, but relying on it for critical side effects creates hidden logic flaws. Attackers can probe for these inconsistencies—like a skipped authentication check or a missed bounds validation—to exploit the program later. Since code reviews and tests often follow the expected execution path, these skipped code blocks become blind spots, turning a language feature into a security weakness. This practice also makes code harder to maintain and reason about. Future developers might modify the conditional logic without realizing that the order of expressions is security-sensitive, inadvertently reintroducing or creating new vulnerabilities. Treating conditional statements as mere checks, rather than sequences of operations, undermines both security and long-term code health.
Impacto en el mundo real

Real-world CVEs caused by CWE-768

Todavía no hay CVEs públicos enlazados a esta CWE en el catálogo de MITRE.

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

The following function attempts to take a size value from a user and allocate an array of that size (we ignore bounds checking for simplicity). The function tries to initialize each spot with the value of its index, that is, A[len-1] = len - 1; A[len-2] = len - 2; ... A[1] = 1; A[0] = 0; However, since the programmer uses the prefix decrement operator, when the conditional is evaluated with i == 1, the decrement will result in a 0 value for the first part of the predicate, causing the second portion to be bypassed via short-circuit evaluation. This means we cannot be sure of what value will be in A[0] when we return the array to the user.

Vulnerable C 
#define PRIV_ADMIN 0
  #define PRIV_REGULAR 1
  typedef struct{
  	int privileges;
  	int id;
  } user_t;
  user_t *Add_Regular_Users(int num_users){
  	user_t* users = (user_t*)calloc(num_users, sizeof(user_t));
  	int i = num_users;
  	while( --i && (users[i].privileges = PRIV_REGULAR) ){
  		users[i].id = i;
  	}
  	return users;
  }
  int main(){
  	user_t* test;
  	int i;
  	test = Add_Regular_Users(25);
  	for(i = 0; i < 25; i++) printf("user %d has privilege level %d\n", test[i].id, test[i].privileges);
  }
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-768

  • Implementation Minimizing the number of statements in a conditional that produce side effects will help to prevent the likelihood of short circuit evaluation to alter control flow in an unexpected way.
Señales de detección

How to detect CWE-768

SAST High

Ejecuta análisis estático (SAST) sobre el código buscando el patrón inseguro en el flujo de datos.

DAST Moderate

Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.

Runtime Moderate

Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.

Code review Moderate

Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-768 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-768?

This vulnerability occurs when a program's conditional statement uses short-circuit evaluation (where later parts of an AND/OR check are skipped if the outcome is already determined), and the skipped portions contain code that changes the program's state. Because these side effects—like updating a variable, checking a permission, or logging an event—are never executed, the application can enter an unexpected and potentially insecure state.

¿Qué gravedad tiene CWE-768?

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-768?

MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.

¿Cómo puedo prevenir CWE-768?

Minimizing the number of statements in a conditional that produce side effects will help to prevent the likelihood of short circuit evaluation to alter control flow in an unexpected way.

¿Cómo detecta y corrige Plexicus CWE-768?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-768 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-768?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/768.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

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Recursos

Further reading

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