CWE-409 Base Incompleto

Improper Handling of Highly Compressed Data (Data Amplification)

This vulnerability occurs when software fails to safely process highly compressed data, where a small input file can trigger the creation of an extremely large amount of data during decompression,…

Definición

What is CWE-409?

This vulnerability occurs when software fails to safely process highly compressed data, where a small input file can trigger the creation of an extremely large amount of data during decompression, overwhelming system resources.
Often called a 'decompression bomb' or 'zip bomb,' this attack exploits the extreme compression ratios possible with formats like ZIP, XML, or PDF. A malicious actor can craft a tiny, harmless-looking file that, when processed by your application, expands to consume gigabytes of memory or disk space, leading to denial of service, crashes, or performance degradation. To prevent this, developers must implement security controls before decompression. This includes setting strict limits on the compression ratio, checking the uncompressed size from file headers before allocating memory, and using streaming decompression with quotas instead of loading entire outputs into memory at once. Treating all compressed input as untrusted and validating its potential impact is a critical step in secure file handling.
Impacto en el mundo real

Real-world CVEs caused by CWE-409

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 XML

The DTD and the very brief XML below illustrate what is meant by an XML bomb. The ZERO entity contains one character, the letter A. The choice of entity name ZERO is being used to indicate length equivalent to that exponent on two, that is, the length of ZERO is 2^0. Similarly, ONE refers to ZERO twice, therefore the XML parser will expand ONE to a length of 2, or 2^1. Ultimately, we reach entity THIRTYTWO, which will expand to 2^32 characters in length, or 4 GB, probably consuming far more data than expected.

Vulnerable XML 
<?xml version="1.0"?>
  <!DOCTYPE MaliciousDTD [
  <!ENTITY ZERO "A">
  <!ENTITY ONE "&ZERO;&ZERO;">
  <!ENTITY TWO "&ONE;&ONE;">
  ...
  <!ENTITY THIRTYTWO "&THIRTYONE;&THIRTYONE;">
  ]>
  <data>&THIRTYTWO;</data>
Payload del atacante

The DTD and the very brief XML below illustrate what is meant by an XML bomb. The ZERO entity contains one character, the letter A. The choice of entity name ZERO is being used to indicate length equivalent to that exponent on two, that is, the length of ZERO is 2^0. Similarly, ONE refers to ZERO twice, therefore the XML parser will expand ONE to a length of 2, or 2^1. Ultimately, we reach entity THIRTYTWO, which will expand to 2^32 characters in length, or 4 GB, probably consuming far more data than expected.

Payload del atacante XML 
<?xml version="1.0"?>
  <!DOCTYPE MaliciousDTD [
  <!ENTITY ZERO "A">
  <!ENTITY ONE "&ZERO;&ZERO;">
  <!ENTITY TWO "&ONE;&ONE;">
  ...
  <!ENTITY THIRTYTWO "&THIRTYONE;&THIRTYONE;">
  ]>
  <data>&THIRTYTWO;</data>
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-409

  • 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-409

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-409 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-409?

This vulnerability occurs when software fails to safely process highly compressed data, where a small input file can trigger the creation of an extremely large amount of data during decompression, overwhelming system resources.

¿Qué gravedad tiene CWE-409?

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-409?

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

¿Cómo puedo prevenir CWE-409?

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-409?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-409 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-409?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/409.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-409

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Recursos

Further reading

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