CWE-40 Variante Rascunho

Path Traversal: '\\UNC\share\name\' (Windows UNC Share)

This vulnerability occurs when an application accepts user input containing a Windows UNC share path (like '\\UNC\share\name') without proper validation, allowing attackers to redirect file…

Definição

What is CWE-40?

This vulnerability occurs when an application accepts user input containing a Windows UNC share path (like '\\UNC\share\name') without proper validation, allowing attackers to redirect file operations to unintended network locations or arbitrary files.
Windows UNC (Universal Naming Convention) paths begin with double backslashes (\\), followed by a server name and share name, enabling network file access. When an application blindly trusts user input containing these paths, attackers can manipulate file reads, writes, or includes to target sensitive files on remote servers or internal network shares they shouldn't have access to. To prevent this, developers should treat UNC paths with the same suspicion as local file paths. Implement strict allow-lists of permitted directories, normalize paths before validation, and run applications with minimal network permissions. Always validate and sanitize user input that references file systems, whether local or networked.
Impacto no mundo real

Real-world CVEs caused by CWE-40

  • CVE-2001-0687

    FTP server allows a remote attacker to retrieve privileged web server system information by specifying arbitrary paths in the UNC format (\\computername\sharename).

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-40

  • Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When validating filenames, use stringent allowlists that limit the character set to be used. If feasible, only allow a single "." character in the filename to avoid weaknesses such as CWE-23, and exclude directory separators such as "/" to avoid CWE-36. Use a list of allowable file extensions, which will help to avoid CWE-434. Do not rely exclusively on a filtering mechanism that removes potentially dangerous characters. This is equivalent to a denylist, which may be incomplete (CWE-184). For example, filtering "/" is insufficient protection if the filesystem also supports the use of "\" as a directory separator. Another possible error could occur when the filtering is applied in a way that still produces dangerous data (CWE-182). For example, if "../" sequences are removed from the ".../...//" string in a sequential fashion, two instances of "../" would be removed from the original string, but the remaining characters would still form the "../" string.
  • Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Sinais de deteção

How to detect CWE-40

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-40 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-40?

This vulnerability occurs when an application accepts user input containing a Windows UNC share path (like '\\UNC\share\name') without proper validation, allowing attackers to redirect file operations to unintended network locations or arbitrary files.

Qual a gravidade do CWE-40?

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-40?

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

Como posso prevenir o CWE-40?

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and…

Como é que o Plexicus deteta e corrige o CWE-40?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-40 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-40?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/40.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-40

CWE-36 Pai

Absolute Path Traversal

This vulnerability occurs when an application builds file paths using user input without properly blocking absolute paths like…

CWE-37 Irmão

Path Traversal: '/absolute/pathname/here'

This vulnerability occurs when an application accepts user input containing absolute file paths (starting with a forward slash like…

CWE-38 Irmão

Path Traversal: '\absolute\pathname\here'

This vulnerability occurs when an application accepts user-supplied input containing Windows-style absolute paths (like…

CWE-39 Irmão

Path Traversal: 'C:dirname'

This vulnerability occurs when an application accepts user input containing Windows drive letters (like 'C:dirname') without proper…

Recursos

Further reading

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