CWE-243 Variante Rascunho High likelihood

Creation of chroot Jail Without Changing Working Directory

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail,…

Definição

What is CWE-243?

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail, attackers can use relative paths to access files and directories that should be restricted.
The chroot() system call isolates a process within a specific directory subtree, known as a jail. However, a critical step is often missed: chroot() does not automatically change the process's current working directory. If the working directory remains outside the new root, any relative path operations (like opening '../etc/passwd') can still traverse the original filesystem, completely bypassing the intended isolation. To properly secure the jail, you must immediately call chdir('/') after chroot(). This changes the working directory to be inside the new root, ensuring all subsequent relative path references are confined. Without this step, the chroot jail provides a false sense of security and is trivial for an attacker to escape.
Impacto no mundo real

Real-world CVEs caused by CWE-243

Ainda não há referências CVE públicas associadas a este CWE no catálogo da MITRE.

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 C

Consider the following source code from a (hypothetical) FTP server:

Vulnerável C 
chroot("/var/ftproot");
  ...
  fgets(filename, sizeof(filename), network);
  localfile = fopen(filename, "r");
  while ((len = fread(buf, 1, sizeof(buf), localfile)) != EOF) {
  	fwrite(buf, 1, sizeof(buf), network);
  }
  fclose(localfile);
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-243

  • 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-243

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-243 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-243?

This vulnerability occurs when a program creates a chroot jail but fails to change its current working directory afterward. Because the process's working directory remains outside the jail, attackers can use relative paths to access files and directories that should be restricted.

Qual a gravidade do CWE-243?

A MITRE classifica a probabilidade de exploração como Alta — esta fraqueza é ativamente explorada em campo e deve ser priorizada para remediação.

Que linguagens ou plataformas são afetadas pelo CWE-243?

MITRE lists the following affected platforms: C, C++, Unix.

Como posso prevenir o CWE-243?

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-243?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-243 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-243?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/243.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

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Recursos

Further reading

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