CWE-336 Variante Rascunho

Same Seed in Pseudo-Random Number Generator (PRNG)

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.

Definição

What is CWE-336?

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.
PRNGs are deterministic, meaning that if you start them from the same seed, they will produce an identical sequence of 'random' numbers every single time. This predictability breaks the core assumption of randomness that many security features rely on, such as session tokens, cryptographic keys, or password reset tokens. If an attacker discovers or can reasonably guess the seed—for example, if it's a hard-coded value, a simple timestamp, or another predictable source—they can pre-calculate or replicate the entire output sequence. This allows them to anticipate future random values, bypass security controls, impersonate users, or compromise encrypted data that depends on those numbers being truly unpredictable.
Impacto no mundo real

Real-world CVEs caused by CWE-336

  • CVE-2022-39218

    SDK for JavaScript app builder for serverless code uses the same fixed seed for a PRNG, allowing cryptography bypass

Como os atacantes a exploram

Trajeto do atacante passo a passo

  1. 1

    The following code uses a statistical PRNG to generate account IDs.

  2. 2

    Because the program uses the same seed value for every invocation of the PRNG, its values are predictable, making the system vulnerable to attack.

  3. 3

    This code attempts to generate a unique random identifier for a user's session.

  4. 4

    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.

  5. 5

    If the user IDs are generated sequentially, or otherwise restricted to a narrow range of values, then this example also exhibits a Small Seed Space (CWE-339).

Exemplo de código vulnerável

Vulnerable Java

The following code uses a statistical PRNG to generate account IDs.

Vulnerável Java 
private static final long SEED = 1234567890;
  public int generateAccountID() {
  	Random random = new Random(SEED);
  	return random.nextInt();
  }
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-336

  • Architecture and Design Do not reuse PRNG seeds. Consider a PRNG that periodically re-seeds itself as needed from a high quality pseudo-random output, such as hardware devices.
  • Architecture and Design / Requirements Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.
Sinais de deteção

How to detect CWE-336

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.)

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-336 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-336?

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) is repeatedly initialized with the same starting seed value.

Qual a gravidade do CWE-336?

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-336?

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

Como posso prevenir o CWE-336?

Do not reuse PRNG seeds. Consider a PRNG that periodically re-seeds itself as needed from a high quality pseudo-random output, such as hardware devices. Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.

Como é que o Plexicus deteta e corrige o CWE-336?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-336 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-336?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/336.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-336

CWE-335 Pai

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-337 Irmão

Predictable Seed in Pseudo-Random Number Generator (PRNG)

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) uses an easily guessable starting value, like the current system…

CWE-339 Irmão

Small Seed Space in PRNG

This vulnerability occurs when a Pseudo-Random Number Generator (PRNG) uses a seed that has too few possible values, making it easy for an…

Recursos

Further reading

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