CWE-271 Classe Incompleto High likelihood

Privilege Dropping / Lowering Errors

This vulnerability occurs when a system or process fails to reduce its elevated permissions before transferring control of a resource to a less-privileged user or component.

Definição

What is CWE-271?

This vulnerability occurs when a system or process fails to reduce its elevated permissions before transferring control of a resource to a less-privileged user or component.
In secure software design, a common practice is for a high-privilege process to perform a sensitive operation and then immediately lower its permissions before interacting with lower-privileged entities. This flaw breaks that chain of trust. When a system hands off a file, process, or network connection without first dropping these elevated rights, it effectively grants those high-level permissions to the receiving party, which may not be authorized to have them. This creates a dangerous privilege escalation path. By failing to contain permissions within their intended scope, the flaw allows excessive access to spread throughout the application environment. An attacker who gains control of the lower-privileged component can then inherit and abuse these unintended permissions, potentially taking full control of the system or accessing restricted data.
Impacto no mundo real

Real-world CVEs caused by CWE-271

  • CVE-2000-1213

    Program does not drop privileges after acquiring the raw socket.

  • CVE-2001-0559

    Setuid program does not drop privileges after a parsing error occurs, then calls another program to handle the error.

  • CVE-2001-0787

    Does not drop privileges in related groups when lowering privileges.

  • CVE-2002-0080

    Does not drop privileges in related groups when lowering privileges.

  • CVE-2001-1029

    Does not drop privileges before determining access to certain files.

  • CVE-1999-0813

    Finger daemon does not drop privileges when executing programs on behalf of the user being fingered.

  • CVE-1999-1326

    FTP server does not drop privileges if a connection is aborted during file transfer.

  • CVE-2000-0172

    Program only uses seteuid to drop privileges.

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

The following code calls chroot() to restrict the application to a subset of the filesystem below APP_HOME in order to prevent an attacker from using the program to gain unauthorized access to files located elsewhere. The code then opens a file specified by the user and processes the contents of the file.

Vulnerável C 
chroot(APP_HOME);
  chdir("/");
  FILE* data = fopen(argv[1], "r+");
  ...
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-271

  • Architecture and Design Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
  • Architecture and Design / Operation Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
  • Architecture and Design Consider following the principle of separation of privilege. Require multiple conditions to be met before permitting access to a system resource.
Sinais de deteção

How to detect CWE-271

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-271 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-271?

This vulnerability occurs when a system or process fails to reduce its elevated permissions before transferring control of a resource to a less-privileged user or component.

Qual a gravidade do CWE-271?

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-271?

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

Como posso prevenir o CWE-271?

Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to…

Como é que o Plexicus deteta e corrige o CWE-271?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-271 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-271?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/271.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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