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,…

Definição

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 no mundo real

Real-world CVEs caused by CWE-409

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    Identificar um caminho de código que trata input não confiável sem validação.

  2. 2

    Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.

  3. 3

    Entregar o payload através de um pedido normal e observar a reação da aplicação.

  4. 4

    Iterar até que a resposta exponha dados, execute código do atacante ou escale privilégios.

Exemplo de código vulnerável

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.

Vulnerável 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 do 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 do 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>
Exemplo 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 verificação de prevenção

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.
Sinais de deteção

How to detect CWE-409

SAST High

Executar análise estática (SAST) na base de código à procura do padrão inseguro no fluxo de dados.

DAST Moderate

Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.

Runtime Moderate

Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.

Code review Moderate

Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-409 e abre um PR de correção em menos de 60 segundos.

O Codex Remedium analisa cada commit, identifica esta fraqueza exata e entrega um pull request pronto para revisão com o patch. Sem tickets. Sem transferências.

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Perguntas frequentes

Frequently asked questions

O que é o 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.

Qual a gravidade do CWE-409?

A MITRE não publicou uma classificação de probabilidade de exploração para esta fraqueza. Trate-a como impacto médio até o seu modelo de ameaças provar o contrário.

Que linguagens ou plataformas são afetadas pelo CWE-409?

A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.

Como posso prevenir o 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.

Como é que o Plexicus deteta e corrige o CWE-409?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-409 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.

Onde posso saber mais sobre o CWE-409?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/409.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-409

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Large Data Table with Excessive Number of Indices

This weakness occurs when an application uses a database table with a very large number of rows and creates too many indexes on it,…

CWE-1094 Irmão

Excessive Index Range Scan for a Data Resource

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CWE-406 Irmão

Insufficient Control of Network Message Volume (Network Amplification)

This vulnerability occurs when a system fails to properly limit the amount of network traffic it can generate in response to a request,…

Recursos

Further reading

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