CWE-638 Clase Borrador

Not Using Complete Mediation

This vulnerability occurs when software fails to verify access permissions every single time a user or process tries to use a resource. Instead, it might rely on a single, outdated check, creating a…

Definición

What is CWE-638?

This vulnerability occurs when software fails to verify access permissions every single time a user or process tries to use a resource. Instead, it might rely on a single, outdated check, creating a security gap if the user's privileges are later revoked or changed.
Complete mediation is the security principle that every access to every object must be checked for authorization. Developers often break this rule by caching an initial permission check—like when a user first opens a file or page—and then assuming that permission remains valid for the entire session. This creates a time-of-check to time-of-use (TOCTOU) window where a user's reduced privileges are not enforced, allowing continued access they should no longer have. To prevent this, implement a consistent authorization layer that validates permissions on each individual request, regardless of previous checks. Treat all access as stateless and never assume a prior grant is still valid. This is especially critical in long-running sessions, multi-step transactions, or systems with dynamic user roles, where privilege changes must be reflected immediately to close security loopholes.
Impacto en el mundo real

Real-world CVEs caused by CWE-638

  • CVE-2007-0408

    Server does not properly validate client certificates when reusing cached connections.

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 pseudo

MITRE no ha publicado un ejemplo de código para esta CWE. El patrón siguiente es ilustrativo — consulta Recursos para referencias canónicas.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
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-638

  • Architecture and Design Invalidate cached privileges, file handles or descriptors, or other access credentials whenever identities, processes, policies, roles, capabilities or permissions change. Perform complete authentication checks before accepting, caching and reusing data, dynamic content and code (scripts). Avoid caching access control decisions as much as possible.
  • Architecture and Design Identify all possible code paths that might access sensitive resources. If possible, create and use a single interface that performs the access checks, and develop code standards that require use of this interface.
Señales de detección

How to detect CWE-638

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-638 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-638?

This vulnerability occurs when software fails to verify access permissions every single time a user or process tries to use a resource. Instead, it might rely on a single, outdated check, creating a security gap if the user's privileges are later revoked or changed.

¿Qué gravedad tiene CWE-638?

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-638?

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

¿Cómo puedo prevenir CWE-638?

Invalidate cached privileges, file handles or descriptors, or other access credentials whenever identities, processes, policies, roles, capabilities or permissions change. Perform complete authentication checks before accepting, caching and reusing data, dynamic content and code (scripts). Avoid caching access control decisions as much as possible. Identify all possible code paths that might access sensitive resources. If possible, create and use a single interface that performs the access…

¿Cómo detecta y corrige Plexicus CWE-638?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-638 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-638?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/638.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-638

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CWE-250 Hermano

Execution with Unnecessary Privileges

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Not Failing Securely ('Failing Open')

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CWE-637 Hermano

Unnecessary Complexity in Protection Mechanism (Not Using 'Economy of Mechanism')

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CWE-653 Hermano

Improper Isolation or Compartmentalization

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CWE-654 Hermano

Reliance on a Single Factor in a Security Decision

This vulnerability occurs when a system's security check depends almost entirely on just one condition, object, or piece of data to decide…

CWE-655 Hermano

Insufficient Psychological Acceptability

This weakness occurs when security features are so cumbersome or confusing that well-intentioned users feel forced to turn them off or…

Recursos

Further reading

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