CWE-34 Variante Incompleto

Path Traversal: '....//'

This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize '....//' sequences. Attackers can use this pattern to break out of the intended…

Definição

What is CWE-34?

This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize '....//' sequences. Attackers can use this pattern to break out of the intended directory and access unauthorized files or folders elsewhere on the system.

The '....//' sequence is a specific evasion technique designed to bypass common path traversal filters. If a security mechanism removes or checks for '../' in a single pass, '....//' can be transformed into '../' after the filter runs, allowing the attack to succeed. This often happens with simple string replacement or certain regular expression implementations that don't account for this overlapping pattern. Attackers use this method when applications try to neutralize '..' sequences or when the operating system treats double slashes ('//') as a single slash. Developers must validate entire canonical paths after normalization, rather than just filtering specific strings, to prevent these bypass attempts. Always resolve user-supplied paths to their absolute location and verify they remain within the permitted directory before any file operation.

Impacto no mundo real

Real-world CVEs caused by CWE-34

CVE-2004-1670

Mail server allows remote attackers to create arbitrary directories via a ".." or rename arbitrary files via a "....//" in user supplied parameters.

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-34

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-34

Automated Static Analysis - Source Code SOAR Partial

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Cost effective for partial coverage: ``` Source code Weakness Analyzer Context-configured Source Code Weakness Analyzer

Architecture or Design Review High

According to SOAR [REF-1479], the following detection techniques may be useful: ``` Highly cost effective: ``` Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.) Formal Methods / Correct-By-Construction

CWE-34

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Perguntas frequentes

Frequently asked questions

O que é o CWE-34?

Qual a gravidade do CWE-34?

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-34?

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

Como posso prevenir o CWE-34?

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-34?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-34 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-34?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/34.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-34

CWE-23 Pai

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Reservar Pentest

Path Traversal: '....//'

What is CWE-34?

Real-world CVEs caused by CWE-34

Trajeto do atacante passo a passo

Vulnerable pseudo

Secure pseudo

How to prevent CWE-34

How to detect CWE-34

Don't catalog this weakness. Prove it's reachable.

Frequently asked questions

Weaknesses related to CWE-34

Relative Path Traversal

Path Traversal: '../filedir'

Path Traversal: '/../filedir'

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

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

Path Traversal: '..\filedir'

Path Traversal: '\..\filename'

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

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

Further reading

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Sample evidence handover

Server-Side Request Forgery in `webhooks/receiver`