CWE-611: Improper Restriction of XML External Entity Reference

Definición

What is CWE-611?

This vulnerability occurs when an application processes XML input without properly restricting external entity references. Attackers can exploit this to read local files, trigger internal network requests, or cause denial of service.

XML parsers often support Document Type Definitions (DTDs), which can define custom entities. When these entities point to external URIs (like file://, http://), the parser may fetch and include that external content. An attacker can inject a malicious DTD that references sensitive system files (e.g., /etc/passwd, C:\Windows\win.ini) or internal endpoints, leading to data exposure or server-side request forgery (SSRF). The retrieved data is often reflected in the application's output, such as error messages or API responses. Preventing XXE requires disabling DTD processing entirely or securely configuring the XML parser to reject external entities. Since manual code reviews and traditional SAST tools can miss parser configurations, managing this at scale is difficult; an ASPM like Plexicus can help you track and remediate these flaws across your entire stack by correlating findings with actual runtime behavior and suggesting prioritized fixes.

Impacto en el mundo real

Real-world CVEs caused by CWE-611

CVE-2022-42745

Recruiter software allows reading arbitrary files using XXE
CVE-2005-1306

A browser control can allow remote attackers to determine the existence of files via Javascript containing XML script.
CVE-2012-5656

XXE during SVG image conversion
CVE-2012-2239

XXE in PHP application allows reading the application's configuration file.
CVE-2012-3489

XXE in database server
CVE-2012-4399

XXE in rapid web application development framework allows reading arbitrary files.
CVE-2012-3363

XXE via XML-RPC request.
CVE-2012-0037

XXE in office document product using RDF.

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-611

Implementation / System Configuration Many XML parsers and validators can be configured to disable external entity expansion.

Señales de detección

How to detect CWE-611

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

CWE-611

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

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-611?

This vulnerability occurs when an application processes XML input without properly restricting external entity references. Attackers can exploit this to read local files, trigger internal network requests, or cause denial of service.

¿Qué gravedad tiene CWE-611?

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-611?

MITRE lists the following affected platforms: XML, Web Based.

¿Cómo puedo prevenir CWE-611?

Many XML parsers and validators can be configured to disable external entity expansion.

¿Cómo detecta y corrige Plexicus CWE-611?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-611 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-611?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/611.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-611

CWE-610 Padre

Listo para validar lo que importa.

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

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Improper Restriction of XML External Entity Reference

What is CWE-611?

Real-world CVEs caused by CWE-611

Ruta del atacante paso a paso

Vulnerable pseudo

Secure pseudo

How to prevent CWE-611

How to detect CWE-611

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

Frequently asked questions

Weaknesses related to CWE-611

Externally Controlled Reference to a Resource in Another Sphere

Improper Restriction of Rendered UI Layers or Frames

External Control of System or Configuration Setting

Session Fixation

Unintended Proxy or Intermediary ('Confused Deputy')

Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

URL Redirection to Untrusted Site ('Open Redirect')

External Control of File Name or Path

Server-Side Request Forgery (SSRF)

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`