CWE-331 Base Rascunho

Insufficient Entropy

This vulnerability occurs when a system's random number generator or algorithm lacks sufficient unpredictability, creating patterns or predictable outputs that are easier for attackers to guess.

Definição

What is CWE-331?

This vulnerability occurs when a system's random number generator or algorithm lacks sufficient unpredictability, creating patterns or predictable outputs that are easier for attackers to guess.

Insufficient entropy means your random values aren't random enough. This often stems from using weak algorithms (like `rand()`), seeding generators with predictable values (like the current time), or drawing from a source with limited possible outcomes. Attackers can exploit these patterns to predict security-critical values like session tokens, cryptographic keys, or password reset codes, effectively bypassing protections that rely on randomness. To prevent this, developers should use cryptographically secure pseudorandom number generators (CSPRNGs) provided by the operating system or language's security libraries. Always ensure your entropy source is robust and unpredictable, especially for initialization vectors, nonces, and key generation. For high-stakes systems, consider using hardware random number generators or dedicated security services to guarantee the quality of your randomness.

Impacto no mundo real

Real-world CVEs caused by CWE-331

CVE-2001-0950

Insufficiently random data used to generate session tokens using C rand(). Also, for certificate/key generation, uses a source that does not block when entropy is low.
CVE-2008-2108

Chain: insufficient precision (CWE-1339) in random-number generator causes some zero bits to be reliably generated, reducing the amount of entropy (CWE-331)

Como os atacantes a exploram

Trajeto do atacante passo a passo

1
This code generates a unique random identifier for a user's session.
2
Because the seed for the PRNG is always the user's ID, the session ID will always be the same. An attacker could thus predict any user's session ID and potentially hijack the session.
3
This example also exhibits a Small Seed Space (CWE-339).
4
The following code uses a statistical PRNG to create a URL for a receipt that remains active for some period of time after a purchase.
5
This code uses the Random.nextInt() function to generate "unique" identifiers for the receipt pages it generates. Because Random.nextInt() is a statistical PRNG, it is easy for an attacker to guess the strings it generates. Although the underlying design of the receipt system is also faulty, it would be more secure if it used a random number generator that did not produce predictable receipt identifiers, such as a cryptographic PRNG.

Exemplo de código vulnerável

Vulnerable PHP

This code generates a unique random identifier for a user's session.

Vulnerável PHP

function generateSessionID($userID){
  	srand($userID);
  	return rand();
  }

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-331

Implementation Determine the necessary entropy to adequately provide for randomness and predictability. This can be achieved by increasing the number of bits of objects such as keys and seeds.

Sinais de deteção

How to detect CWE-331

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-331 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.

Obter uma demonstração Experimente o Plexicus gratuitamente

Perguntas frequentes

Frequently asked questions

O que é o CWE-331?

This vulnerability occurs when a system's random number generator or algorithm lacks sufficient unpredictability, creating patterns or predictable outputs that are easier for attackers to guess.

Qual a gravidade do CWE-331?

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-331?

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

Como posso prevenir o CWE-331?

Determine the necessary entropy to adequately provide for randomness and predictability. This can be achieved by increasing the number of bits of objects such as keys and seeds.

Como é que o Plexicus deteta e corrige o CWE-331?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-331 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-331?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/331.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-331

CWE-330 Pai

Use of Insufficiently Random Values

This vulnerability occurs when an application uses random values that are not sufficiently unpredictable in security-sensitive operations,…

CWE-1204 Irmão

Generation of Weak Initialization Vector (IV)

This vulnerability occurs when software uses a weak or predictable Initialization Vector (IV) for cryptographic operations. Many…

CWE-1241 Irmão

Use of Predictable Algorithm in Random Number Generator

This vulnerability occurs when a device or application relies on a predictable algorithm to generate pseudo-random numbers, making the…

CWE-334 Irmão

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…

CWE-335 Irmão

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

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is used, but its initial seed value is not handled securely or…

CWE-338 Irmão

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

This vulnerability occurs when software uses a pseudo-random number generator (PRNG) that is not cryptographically strong for…

CWE-340 Irmão

Generation of Predictable Numbers or Identifiers

This vulnerability occurs when a system creates numbers or identifiers that are too easy to guess, undermining security mechanisms that…

CWE-344 Irmão

Use of Invariant Value in Dynamically Changing Context

This vulnerability occurs when code uses a fixed, unchanging value (like a hardcoded string, number, or reference) in a situation where…

CWE-332 Filho