CWE-334 Base Rascunho

Small Space of Random Values

This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict or guess these values through brute force attacks.

Definição

What is CWE-334?

This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict or guess these values through brute force attacks.

When an application relies on random values for security—like generating session tokens, encryption keys, or password reset codes—using a random source with a small output space is a critical flaw. For example, a random number generator that only produces 65,536 possible values (16 bits) is trivial for an automated script to exhaustively try all combinations. This directly undermines security mechanisms designed to be unpredictable. To prevent this, developers must ensure their random value generators have an output space large enough to resist brute-force attempts for the required lifespan of the secret. This typically means using cryptographically secure pseudo-random number generators (CSPRNGs) that produce values with at least 128 bits of entropy. Always match the randomness strength to the sensitivity of the operation it protects.

Impacto no mundo real

Real-world CVEs caused by CWE-334

CVE-2002-0583

Product uses 5 alphanumeric characters for filenames of expense claim reports, stored under web root.
CVE-2002-0903

Product uses small number of random numbers for a code to approve an action, and also uses predictable new user IDs, allowing attackers to hijack new accounts.
CVE-2003-1230

SYN cookies implementation only uses 32-bit keys, making it easier to brute force ISN.
CVE-2004-0230

Complex predictability / randomness (reduced space).

Como os atacantes a exploram

Trajeto do atacante passo a passo

1
The following XML example code is a deployment descriptor for a Java web application deployed on a Sun Java Application Server. This deployment descriptor includes a session configuration property for configuring the session ID length.
2
This deployment descriptor has set the session ID length for this Java web application to 8 bytes (or 64 bits). The session ID length for Java web applications should be set to 16 bytes (128 bits) to prevent attackers from guessing and/or stealing a session ID and taking over a user's session.
3
Note for most application servers including the Sun Java Application Server the session ID length is by default set to 128 bits and should not be changed. And for many application servers the session ID length cannot be changed from this default setting. Check your application server documentation for the session ID length default setting and configuration options to ensure that the session ID length is set to 128 bits.

Exemplo de código vulnerável

Vulnerable XML

The following XML example code is a deployment descriptor for a Java web application deployed on a Sun Java Application Server. This deployment descriptor includes a session configuration property for configuring the session ID length.

Vulnerável XML

<sun-web-app>
  		...
  		<session-config>
  				<session-properties>
  					<property name="idLengthBytes" value="8">
  						<description>The number of bytes in this web module's session ID.</description>
  					</property>
  				</session-properties>
  		</session-config>
  		...
  </sun-web-app>

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-334

Architecture and Design / Requirements Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").

Sinais de deteção

How to detect CWE-334

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.

CWE-334

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Perguntas frequentes

Frequently asked questions

O que é o CWE-334?

This vulnerability occurs when a system uses a random number generator that produces too few possible values. Attackers can easily predict or guess these values through brute force attacks.

Qual a gravidade do CWE-334?

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-334?

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

Como posso prevenir o CWE-334?

Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems. Consult FIPS 140-2 Annex C ("Approved Random Number Generators").

Como é que o Plexicus deteta e corrige o CWE-334?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-334 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-334?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/334.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-334

CWE-330 Pai

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Small Space of Random Values

What is CWE-334?

Real-world CVEs caused by CWE-334

Trajeto do atacante passo a passo

Vulnerable XML

Secure pseudo

How to prevent CWE-334

How to detect CWE-334

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

Frequently asked questions

Weaknesses related to CWE-334

Use of Insufficiently Random Values

Generation of Weak Initialization Vector (IV)

Use of Predictable Algorithm in Random Number Generator

Insufficient Entropy

Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)

Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)

Generation of Predictable Numbers or Identifiers

Use of Invariant Value in Dynamically Changing Context

J2EE Misconfiguration: Insufficient Session-ID Length

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`