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
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…
Definición
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 en el mundo real
Real-world CVEs caused by CWE-34
-
Mail server allows remote attackers to create arbitrary directories via a ".." or rename arbitrary files via a "....//" in user supplied parameters.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
Identifica una ruta de código que maneje entrada no confiable sin validación.
- 2
Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.
- 3
Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.
- 4
Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.
Ejemplo de código vulnerable
Vulnerable pseudo
MITRE no ha publicado un ejemplo de código para esta CWE. El patrón siguiente es ilustrativo — consulta Recursos para referencias canónicas.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Ejemplo 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 prevención
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.
Señales de detección
How to detect CWE-34
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
Plexicus detecta automáticamente CWE-34 y abre un PR de corrección en menos de 60 segundos.
Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.
Preguntas frecuentes ¿Qué es CWE-34?
¿Qué gravedad tiene CWE-34?
¿Qué lenguajes o plataformas se ven afectados por CWE-34?
¿Cómo puedo prevenir CWE-34?
¿Cómo detecta y corrige Plexicus CWE-34?
¿Dónde puedo aprender más sobre CWE-34?
Frequently asked questions
¿Qué es 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.
¿Qué gravedad tiene CWE-34?
MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.
¿Qué lenguajes o plataformas se ven afectados por CWE-34?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir 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…
¿Cómo detecta y corrige Plexicus CWE-34?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-34 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.
¿Dónde puedo aprender más sobre CWE-34?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/34.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-34
CWE-23 Padre
Relative Path Traversal
This vulnerability occurs when an application builds file paths using user-supplied input without properly validating or sanitizing it.…
CWE-24 Hermano
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 Hermano
Path Traversal: '/../filedir'
This vulnerability, often called directory traversal, occurs when an application builds a file path using user input without properly…
CWE-26 Hermano
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 Hermano
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 Hermano
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 Hermano
Path Traversal: '\..\filename'
This vulnerability occurs when an application builds file paths using user input but fails to block '\..\filename' sequences. Attackers…
CWE-30 Hermano
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 Hermano
Path Traversal: 'dir\..\..\filename'
This vulnerability occurs when an application builds file paths using user input but fails to properly block sequences like…
Recursos
Further reading
- MITRE — CWE-34 oficial https://cwe.mitre.org/data/definitions/34.html
- State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation https://www.ida.org/-/media/feature/publications/s/st/stateoftheart-resources-soar-for-software-vulnerability-detection-test-and-evaluation/p-5061.ashx
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