CWE-57 Variante Incompleto

Path Equivalence: 'fakedir/../realdir/filename'

This vulnerability occurs when an application uses external input to build file paths, allowing attackers to bypass access controls. By submitting a path like 'fakedir/../realdir/filename', they can…

Definición

What is CWE-57?

This vulnerability occurs when an application uses external input to build file paths, allowing attackers to bypass access controls. By submitting a path like 'fakedir/../realdir/filename', they can navigate out of a restricted directory ('fakedir') and into a protected one ('realdir'), accessing files the security mechanisms were designed to block.
This flaw is a specific type of path traversal attack where the security check fails due to how the path is interpreted. The application might correctly validate or restrict access to the direct path 'realdir/filename'. However, it doesn't account for directory traversal sequences ('../') being prepended. When it concatenates user input like 'fakedir/../realdir/filename' without proper normalization, the system resolves the '..' to move up a directory, effectively making the 'fakedir' part irrelevant and granting access to the real target. To prevent this, developers must implement canonicalization or path normalization before applying any security checks. This process resolves all '..' and '.' sequences and symbolic links to produce a single, absolute, and clean path. Access controls should then be applied to this final, normalized path, ensuring that any crafted input with traversal sequences is evaluated based on the actual file or directory it points to, not the deceptive path structure provided by the user.
Impacto en el mundo real

Real-world CVEs caused by CWE-57

  • CVE-2001-1152

    Proxy allows remote attackers to bypass denylist restrictions and connect to unauthorized web servers by modifying the requested URL, including (1) a // (double slash), (2) a /SUBDIR/.. where the desired file is in the parentdir, (3) a /./, or (4) URL-encoded characters.

  • CVE-2000-0191

    application check access for restricted URL before canonicalization

  • CVE-2005-1366

    CGI source disclosure using "dirname/../cgi-bin"

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-57

  • Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Señales de detección

How to detect CWE-57

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-57 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-57?

This vulnerability occurs when an application uses external input to build file paths, allowing attackers to bypass access controls. By submitting a path like 'fakedir/../realdir/filename', they can navigate out of a restricted directory ('fakedir') and into a protected one ('realdir'), accessing files the security mechanisms were designed to block.

¿Qué gravedad tiene CWE-57?

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-57?

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

¿Cómo puedo prevenir CWE-57?

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

¿Cómo detecta y corrige Plexicus CWE-57?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-57 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-57?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/57.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-57

CWE-41 Padre

Improper Resolution of Path Equivalence

This vulnerability occurs when an application fails to properly handle different text representations that refer to the same file or…

CWE-42 Hermano

Path Equivalence: 'filename.' (Trailing Dot)

This vulnerability occurs when a system accepts file or directory paths that end with a dot (like 'file.txt.' or 'folder.') without…

CWE-44 Hermano

Path Equivalence: 'file.name' (Internal Dot)

This vulnerability occurs when an application accepts file paths containing internal dots (like 'file.ordir') without properly checking…

CWE-46 Hermano

Path Equivalence: 'filename ' (Trailing Space)

This vulnerability occurs when an application processes file paths that end with a space character (like 'document.txt ') without properly…

CWE-47 Hermano

Path Equivalence: ' filename' (Leading Space)

This vulnerability occurs when an application accepts file or directory paths that begin with a space character (like ' filename'),…

CWE-48 Hermano

Path Equivalence: 'file name' (Internal Whitespace)

This vulnerability occurs when an application accepts file paths containing internal spaces (like 'file name') without proper validation.…

CWE-49 Hermano

Path Equivalence: 'filename/' (Trailing Slash)

This vulnerability occurs when an application accepts file or directory paths that end with a slash (e.g., 'documents/') without properly…

CWE-50 Hermano

Path Equivalence: '//multiple/leading/slash'

This vulnerability occurs when an application accepts file or directory paths containing multiple leading slashes (like…

CWE-51 Hermano

Path Equivalence: '/multiple//internal/slash'

This vulnerability occurs when an application accepts file or directory paths containing multiple consecutive forward slashes (e.g.,…

Recursos

Further reading

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