CWE-28 Variante Incompleto

Path Traversal: '..\filedir'

This vulnerability occurs when an application builds a file path using user input but fails to block or properly handle '..\' sequences. This oversight allows an attacker to break out of the…

Definição

What is CWE-28?

This vulnerability occurs when an application builds a file path using user input but fails to block or properly handle '..\' sequences. This oversight allows an attacker to break out of the intended directory and navigate to unauthorized locations in the file system.

Attackers exploit this flaw by injecting '..\' (dot-dot-backslash) sequences into file path parameters. Since each '..\' moves up one directory level, they can craft a path like '..\..\windows\system32\config' to access sensitive files well outside the application's allowed directory, potentially leading to data theft, system information disclosure, or server compromise. While this sequence is specific to Windows systems that use the backslash (\) as a separator, it's a critical bypass technique. Many defensive filters only check for the forward slash (/) used in Unix-style paths, making the '..\' variant a common method for evading simple validation and achieving the same traversal effect on Windows servers.

Impacto no mundo real

Real-world CVEs caused by CWE-28

CVE-2002-0661

"\" not in denylist for web server, allowing path traversal attacks when the server is run in Windows and other OSes.
CVE-2002-0946

Arbitrary files may be read files via ..\ (dot dot) sequences in an HTTP request.
CVE-2002-1042

Directory traversal vulnerability in search engine for web server allows remote attackers to read arbitrary files via "..\" sequences in queries.
CVE-2002-1209

Directory traversal vulnerability in FTP server allows remote attackers to read arbitrary files via "..\" sequences in a GET request.
CVE-2002-1178

Directory traversal vulnerability in servlet allows remote attackers to execute arbitrary commands via "..\" sequences in an HTTP request.

Como os atacantes a exploram

Trajeto do atacante passo a passo

1
Identificar um caminho de código que trata input não confiável sem validação.
2
Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.
3
Entregar o payload através de um pedido normal e observar a reação da aplicação.
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-28

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-28

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-28 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.

Obter uma demonstração Experimente o Plexicus gratuitamente

Perguntas frequentes

Frequently asked questions

O que é o CWE-28?

Qual a gravidade do CWE-28?

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-28?

MITRE lists the following affected platforms: Windows.

Como posso prevenir o CWE-28?

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-28?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-28 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-28?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/28.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-28

CWE-23 Pai

Relative Path Traversal

This vulnerability occurs when an application builds file paths using user-supplied input without properly validating or sanitizing it.…

CWE-24 Irmão

Path Traversal: '../filedir'

Path traversal, often called directory traversal, occurs when an application builds a file path using user input without properly blocking…

CWE-25 Irmão

Path Traversal: '/../filedir'

This vulnerability, often called directory traversal, occurs when an application builds a file path using user input without properly…

CWE-26 Irmão

Path Traversal: '/dir/../filename'

This vulnerability occurs when an application builds a file path using user input but fails to properly block directory traversal…

CWE-27 Irmão

Path Traversal: 'dir/../../filename'

This vulnerability occurs when an application builds file paths using user input but fails to properly block sequences like…

CWE-29 Irmão

Path Traversal: '\..\filename'

This vulnerability occurs when an application builds file paths using user input but fails to block '\..\filename' sequences. Attackers…

CWE-30 Irmão

Path Traversal: '\dir\..\filename'

This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize sequences like…

CWE-31 Irmão

Path Traversal: 'dir\..\..\filename'