CWE-26 Variante Borrador

Path Traversal: '/dir/../filename'

Definición

What is CWE-26?

This vulnerability occurs when an application builds a file path using user input but fails to properly block directory traversal sequences like '/dir/../filename'. This allows an attacker to break out of the intended restricted directory and access files or folders elsewhere on the system.

Attackers exploit this weakness to navigate the server's file system and read, write, or delete sensitive files outside the application's allowed directory. This is a classic path traversal attack, but the specific '/dir/../filename' pattern is often used to bypass simple security filters that only check for '../' at the very beginning of the input string. Developers can prevent this by using strong, canonical path validation. Instead of just checking for '..', your code should resolve the entire input path to its absolute, canonical form and then verify it remains strictly within the intended base directory. Relying on built-in language APIs for path normalization and sandboxing is far safer than trying to manually filter out specific sequences.

Impacto en el mundo real

Real-world CVEs caused by CWE-26

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
Identifica una ruta de código que maneje entrada no confiable sin validación.
2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
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-26

Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would be removed from the original string, but the remaining characters would still form the "../" string.
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-26

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.

CWE-26

Don't catalog this weakness. Prove it's reachable.

Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-26?

¿Qué gravedad tiene CWE-26?

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-26?

MITRE lists the following affected platforms: Web Server.

¿Cómo puedo prevenir CWE-26?

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and…

¿Cómo detecta y corrige Plexicus CWE-26?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-26 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-26?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/26.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-26

CWE-23 Padre

Listo para validar lo que importa.

Plexicus es Proof-Driven AppSec: hallazgos validados, comprensión contextual y remediación revisada — anclada en evidencia, acotada contigo.

Reservar Pentest

Path Traversal: '/dir/../filename'

What is CWE-26?

Real-world CVEs caused by CWE-26

Ruta del atacante paso a paso

Vulnerable pseudo

Secure pseudo

How to prevent CWE-26

How to detect CWE-26

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-26

Relative Path Traversal

Path Traversal: '../filedir'

Path Traversal: '/../filedir'

Path Traversal: 'dir/../../filename'

Path Traversal: '..\filedir'

Path Traversal: '\..\filename'

Path Traversal: '\dir\..\filename'

Path Traversal: 'dir\..\..\filename'

Path Traversal: '...' (Triple Dot)

Further reading

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Comprueba si el AI Swarm Pentest encaja en tu entorno.

Solicitud recibida. Reserva el siguiente paso.

Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`