CWE-689 Compuesto Borrador

Permission Race Condition During Resource Copy

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains…

Definición

What is CWE-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.
This race condition is a classic time-of-check to time-of-use (TOCTOU) flaw specific to resource duplication. When an application copies a file—for example, during installation, backup, or user upload—it often creates the new file with broad default permissions (like world-readable) to ensure the copy succeeds. The intended restrictive permissions are only applied after the data transfer is complete. This gap, however brief, is a real security risk, especially on multi-user systems or shared hosting environments where other processes are actively running. To prevent this, developers should implement atomic operations where possible, such as creating the file with the correct permissions from the outset before writing data. Alternatively, copy operations can be performed in a secure, isolated temporary location with strict access controls, and the file should only be moved to its final destination after both the data and the correct permissions are fully applied, eliminating the exposure window.
Impacto en el mundo real

Real-world CVEs caused by CWE-689

  • CVE-2002-0760

    Archive extractor decompresses files with world-readable permissions, then later sets permissions to what the archive specified.

  • CVE-2005-2174

    Product inserts a new object into database before setting the object's permissions, introducing a race condition.

  • CVE-2006-5214

    Error file has weak permissions before a chmod is performed.

  • CVE-2005-2475

    Archive permissions issue using hard link.

  • CVE-2003-0265

    Database product creates files world-writable before initializing the setuid bits, leading to modification of executables.

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-689

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Señales de detección

How to detect CWE-689

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-689 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-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.

¿Qué gravedad tiene CWE-689?

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-689?

MITRE lists the following affected platforms: C, Perl.

¿Cómo puedo prevenir CWE-689?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

¿Cómo detecta y corrige Plexicus CWE-689?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-689 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-689?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/689.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-689

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Recursos

Further reading

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