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CWE-35 Variante Incompleto
Path Traversal: '.../...//'
This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize the '.../...//' sequence. Attackers can use this specific pattern to break out of the…
Definição
What is CWE-35?
This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize the '.../...//' sequence. Attackers can use this specific pattern to break out of the intended directory and access unauthorized files or folders elsewhere on the system.
Attackers use the '.../...//' sequence to bypass common path traversal filters. If a security filter removes '../' strings one at a time (a technique called sequential stripping), this clever pattern can trick the filter. The first removal turns '.../...//' into '....//', and the second removal transforms it back into the dangerous '../' payload, effectively bypassing the protection.
Understanding this nuance is critical for defense. Your application might be vulnerable to this specific bypass (CWE-35) even if it's protected against standard '../' attacks (CWE-34), or vice-versa. Effective protection requires canonicalizing the path before checking or filtering, rather than relying on simple sequential string removal.
Impacto no mundo real
Real-world CVEs caused by CWE-35
-
chain: ".../...//" bypasses protection mechanism using regexp's that remove "../" resulting in collapse into an unsafe value "../" (CWE-182) and resultant path traversal.
-
".../....///" bypasses regexp's that remove "./" and "../"
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.
// 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
// 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-35
- 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-35
Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.
Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.
Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.
CWE-35
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Perguntas frequentes O que é o CWE-35?
Qual a gravidade do CWE-35?
Que linguagens ou plataformas são afetadas pelo CWE-35?
Como posso prevenir o CWE-35?
Como é que o Plexicus deteta e corrige o CWE-35?
Onde posso saber mais sobre o CWE-35?
Frequently asked questions
O que é o CWE-35?
This vulnerability occurs when an application builds file paths using user input but fails to properly sanitize the '.../...//' sequence. Attackers can use this specific pattern to break out of the intended directory and access unauthorized files or folders elsewhere on the system.
Qual a gravidade do CWE-35?
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-35?
A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.
Como posso prevenir o CWE-35?
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-35?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-35 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-35?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/35.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
Weaknesses related to CWE-35
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-28 Irmão
Path Traversal: '..\filedir'
This vulnerability occurs when an application builds a file path using user input but fails to block or properly handle '..\' sequences.…
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'
This vulnerability occurs when an application builds file paths using user input but fails to properly block sequences like…
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