CWE-689 Composto Rascunho

Permission Race Condition During Resource Copy

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains…

Definição

What is CWE-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.
This race condition is a classic time-of-check to time-of-use (TOCTOU) flaw specific to resource duplication. When an application copies a file—for example, during installation, backup, or user upload—it often creates the new file with broad default permissions (like world-readable) to ensure the copy succeeds. The intended restrictive permissions are only applied after the data transfer is complete. This gap, however brief, is a real security risk, especially on multi-user systems or shared hosting environments where other processes are actively running. To prevent this, developers should implement atomic operations where possible, such as creating the file with the correct permissions from the outset before writing data. Alternatively, copy operations can be performed in a secure, isolated temporary location with strict access controls, and the file should only be moved to its final destination after both the data and the correct permissions are fully applied, eliminating the exposure window.
Impacto no mundo real

Real-world CVEs caused by CWE-689

  • CVE-2002-0760

    Archive extractor decompresses files with world-readable permissions, then later sets permissions to what the archive specified.

  • CVE-2005-2174

    Product inserts a new object into database before setting the object's permissions, introducing a race condition.

  • CVE-2006-5214

    Error file has weak permissions before a chmod is performed.

  • CVE-2005-2475

    Archive permissions issue using hard link.

  • CVE-2003-0265

    Database product creates files world-writable before initializing the setuid bits, leading to modification of executables.

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 pseudo

A MITRE não publicou um exemplo de código para este CWE. O padrão abaixo é ilustrativo — consulte os Recursos para referências canónicas.

Vulnerável pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
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-689

  • 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-689

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-689 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-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.

Qual a gravidade do CWE-689?

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-689?

MITRE lists the following affected platforms: C, Perl.

Como posso prevenir o CWE-689?

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-689?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-689 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-689?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/689.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-689

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Recursos

Further reading

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